How to create an array containing 1 N

Question

I m looking for any alternatives to the below for creating a JavaScript array containing 1 through to N where N is only known at runtime  var foo        for  var i   1  i  lt   N  i         foo push i      To me it feels like there should be a way of doing this without the loop

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I was looking for a functional solution and I ended up with   function numbers min  max      return Array max-min 2  join   split      map function e  i    return min i         console log numbers 1  9      Note  join   split      transforms the sparse array into a contiguous one

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Try this    var foo    1  2  3  4  5     If you are using CoffeeScript  you can create a range by doing   var foo    1  5      Otherwise  if you are using vanilla JavaScript  you ll have to use a loop if you want to initialize an array up to a variable length

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for me this is more useful utility          create an array filled with integer numbers from base to length     param  number  from     param  number  to     param  number  increment     param  Array  exclude     return  Array      export const count    from   0  to   1  increment   1  exclude         gt      const array         for  let i   from  i  lt   to  i    increment   exclude includes i   amp  amp  array push i     return array

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In ES6 you can do   Array N  fill   map  e i   gt i 1    http   jsbin com molabiluwa edit js console  Edit  Changed Array 45  to Array N  since you ve updated the question    x000D   x000D  console log  x000D    Array 45  fill 0  map  e i   gt i 1  x000D     x000D   x000D   x000D

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You can use a function generator or function  expression  Here s  https   developer mozilla org en-US docs Web JavaScript Reference Operators function  And a reference to the function generator link to  https   developer mozilla org en-US docs Web JavaScript Reference Statements function    let a   1  b   10   function  range a  b      for  var i   a  i  lt   b    i  yield i     Array from range a  b        1  2  3  4  5  6  7  8  9  10       range a  b       1  2  3  4  5  6  7  8  9  10

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repeat 5  split     map     i    gt  i   1  will yield  1  2  3  4  5

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Array 8  fill 0  map Number call  Number    Stealing Igors Number call trick but using fill   to shorten slightly  Only works with ES6 and above

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no for create array in ES6 solutions  js no for 100 array  1  padStart     string arr const arr          padStart 100        map  item  i    gt  i   1             100    quot 1 quot    quot 2 quot    quot 3 quot    quot 4 quot    quot 5 quot    quot 6 quot    quot 7 quot    quot 8 quot    quot 9 quot    quot 10 quot    quot 11 quot    quot 12 quot    quot 13 quot    quot 14 quot    quot 15 quot    quot 16 quot    quot 17 quot    quot 18 quot    quot 19 quot    quot 20 quot    quot 21 quot    quot 22 quot    quot 23 quot    quot 24 quot    quot 25 quot    quot 26 quot    quot 27 quot    quot 28 quot    quot 29 quot    quot 30 quot    quot 31 quot    quot 32 quot    quot 33 quot    quot 34 quot    quot 35 quot    quot 36 quot    quot 37 quot    quot 38 quot    quot 39 quot    quot 40 quot    quot 41 quot    quot 42 quot    quot 43 quot    quot 44 quot    quot 45 quot    quot 46 quot    quot 47 quot    quot 48 quot    quot 49 quot    quot 50 quot    quot 51 quot    quot 52 quot    quot 53 quot    quot 54 quot    quot 55 quot    quot 56 quot    quot 57 quot    quot 58 quot    quot 59 quot    quot 60 quot    quot 61 quot    quot 62 quot    quot 63 quot    quot 64 quot    quot 65 quot    quot 66 quot    quot 67 quot    quot 68 quot    quot 69 quot    quot 70 quot    quot 71 quot    quot 72 quot    quot 73 quot    quot 74 quot    quot 75 quot    quot 76 quot    quot 77 quot    quot 78 quot    quot 79 quot    quot 80 quot    quot 81 quot    quot 82 quot    quot 83 quot    quot 84 quot    quot 85 quot    quot 86 quot    quot 87 quot    quot 88 quot    quot 89 quot    quot 90 quot    quot 91 quot    quot 92 quot    quot 93 quot    quot 94 quot    quot 95 quot    quot 96 quot    quot 97 quot    quot 98 quot    quot 99 quot    quot 100 quot        number arr const arr          padStart 100        map  item  i    gt  i   1        100   1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64  65  66  67  68  69  70  71  72  73  74  75  76  77  78  79  80  81  82  83  84  85  86  87  88  89  90  91  92  93  94  95  96  97  98  99  100     2  Typed Arrays  Uint8Array     number arr const arr   new Uint8Array 100  map  item  i    gt  i   1       Uint8Array 100    1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64  65  66  67  68  69  70  71  72  73  74  75  76  77  78  79  80  81  82  83  84  85  86  87  88  89  90  91  92  93  94  95  96  97  98  99  100      string arr const arr       new Uint8Array 100  map  item  i    gt  i   1   map  item  i    gt  i   1             100    quot 1 quot    quot 2 quot    quot 3 quot    quot 4 quot    quot 5 quot    quot 6 quot    quot 7 quot    quot 8 quot    quot 9 quot    quot 10 quot    quot 11 quot    quot 12 quot    quot 13 quot    quot 14 quot    quot 15 quot    quot 16 quot    quot 17 quot    quot 18 quot    quot 19 quot    quot 20 quot    quot 21 quot    quot 22 quot    quot 23 quot    quot 24 quot    quot 25 quot    quot 26 quot    quot 27 quot    quot 28 quot    quot 29 quot    quot 30 quot    quot 31 quot    quot 32 quot    quot 33 quot    quot 34 quot    quot 35 quot    quot 36 quot    quot 37 quot    quot 38 quot    quot 39 quot    quot 40 quot    quot 41 quot    quot 42 quot    quot 43 quot    quot 44 quot    quot 45 quot    quot 46 quot    quot 47 quot    quot 48 quot    quot 49 quot    quot 50 quot    quot 51 quot    quot 52 quot    quot 53 quot    quot 54 quot    quot 55 quot    quot 56 quot    quot 57 quot    quot 58 quot    quot 59 quot    quot 60 quot    quot 61 quot    quot 62 quot    quot 63 quot    quot 64 quot    quot 65 quot    quot 66 quot    quot 67 quot    quot 68 quot    quot 69 quot    quot 70 quot    quot 71 quot    quot 72 quot    quot 73 quot    quot 74 quot    quot 75 quot    quot 76 quot    quot 77 quot    quot 78 quot    quot 79 quot    quot 80 quot    quot 81 quot    quot 82 quot    quot 83 quot    quot 84 quot    quot 85 quot    quot 86 quot    quot 87 quot    quot 88 quot    quot 89 quot    quot 90 quot    quot 91 quot    quot 92 quot    quot 93 quot    quot 94 quot    quot 95 quot    quot 96 quot    quot 97 quot    quot 98 quot    quot 99 quot    quot 100 quot

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I didn t see any solution based on recursive functions  and never wrote recursive functions myself  so here is my try   Note that array push something  returns the new length of the array     a     push a push a push 0        a    0  1  2    And with a recursive function   var a    function f s e a n  return   n n n s  gt e  a f s e a a a    a push n  s    start end     e g   start   1  end   5   EDIT   two other solutions  var a   Object keys new Int8Array 6   map Number  slice 1    and  var a      var i setInterval function   a length   5 clearInterval i  a push a length 1

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Iterable version using a generator function that doesn t modify Number prototype    x000D   x000D  function sequence max  step   1    x000D    return   x000D       Symbol iterator   function       x000D        for  let i   1  i  lt   max  i    step  yield i x000D        x000D      x000D    x000D   x000D  console log     sequence 10    x000D   x000D   x000D

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Array from   length   stop - start    step   1       i    gt  start    i   step      Source  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Array from

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Let s share mine  p Math pow 2  10  toString 2  split     slice 1  map    j    gt    j

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Object keys Array apply 0  Array 3    map Number  Returns  0  1  2   Very similar to Igor Shubin s excellent answer  but with slightly less trickery  and one character longer   Explanation   Array 3      undefined    3  Generate an array of length n 3  Unfortunately this array is almost useless to us  so we have to    Array apply 0 Array 3       undefined  undefined  undefined  make the array iterable  Note  null s more common as apply s first arg but 0 s shorter  Object keys Array apply 0 Array 3         0    1    2   then get the keys of the array  works because Arrays are the typeof array is an object with indexes for keys  Object keys Array apply 0 Array 3    map Number      0  1  2  and map over the keys  converting strings to numbers

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In ES6   Array from  length  1000       i    gt  i  slice 1     or better yet  without the extra variable   and without the extra slice call    Array from  length 1000   Number call  i   gt  i   1    Or for slightly faster results  you can use Uint8Array  if your list is shorter than 256 results  or you can use the other Uint lists depending on how short the list is  like Uint16 for a max number of  65535  or Uint32 for a max of 4294967295 etc  Officially  these typed arrays were only added in ES6 though   For example   Uint8Array from  length 10   Number call  i   gt  i   1    ES5   Array apply 0   length  1000   map function   return arguments 1  1      Alternatively  in ES5  for the map function  like second parameter to the Array from function in ES6 above   you can use Number call  Array apply 0  length 1000   map Number call Number  slice 1    Or  if you re against the  slice here also  you can do the ES5 equivalent of the above  from ES6   like   Array apply 0  length 1000   map Number call  Function  i   return i 1

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All of these are too complicated  Just do   function count num      var arr         var i   0     while  num--        arr push i            return arr     console log count 9       gt    0  1  2  3  4  5  6  7  8     Or to do a range from a to b  function range a  b      var arr          while  a  lt  b   1        arr push a            return arr     console log range 4  9       gt    4  5  6  7  8  9

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The least codes I could produce   for foo  x 100   x  foo x-1  x--   console log foo

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A little bit simpler than the string variant      create range by N Array N  join 0  split 0       create a range starting with 0 as the value Array 7  join 0  split 0  map  v  i    gt  i   1      1  2  3  4  5  6  7    Update  1 4 2018   Updated to address the exact OP question  Thanks  lessless for calling this out

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with ES6 you can do       n  is the size you want to initialize your array     null  is what the array will be filled with  can be any other value  Array n  fill null

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the fastest way to fill an Array in v8 is       Array 5   map    i    gt  i     result will be   0  1  2  3  4

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https   stackoverflow com a 49577331 8784402 With Delta For javascript smallest and one-liner     Array N   map  v  i    gt  from   i   step    Examples and other alternatives Array from Array 10  keys    map i   gt  4   i   2       gt   4  6  8  10  12  14  16  18  20  22       Array 10  keys    map i   gt  4   i   -2       gt   4  2  0  -2  -4  -6  -8  -10  -12  -14   Array 10  fill 0  map  v  i    gt  4   i   2       gt   4  6  8  10  12  14  16  18  20  22   Array 10  fill   map  v  i    gt  4   i   -2       gt   4  2  0  -2  -4  -6  -8  -10  -12  -14       Array 10   map  v  i    gt  4   i   2       gt   4  6  8  10  12  14  16  18  20  22   Range Function const range    from  to  step    gt        Array Math floor  to - from    step    1   map     i    gt  from   i   step    range 0  9  2       gt   0  2  4  6  8      can also assign range function as static method in Array class  but not recommended   Array range    from  to  step    gt        Array Math floor  to - from    step    1   map     i    gt  from   i   step    Array range 2  10  2       gt   2  4  6  8  10   Array range 0  10  1       gt   0  1  2  3  4  5  6  7  8  9  10   Array range 2  10  -1       gt      Array range 3  0  -1       gt   3  2  1  0   As Iterators class Range     constructor total   0  step   1  from   0        this Symbol iterator    function             for  let i   0  i  lt  total  yield from   i     step                       new Range 5       Five Elements     gt    0  1  2  3  4      new Range 5  2       Five Elements With Step 2     gt    0  2  4  6  8      new Range 5  -2  10       Five Elements With Step -2 From 10     gt  10  8  6  4  2      new Range 5  -2  -10       Five Elements With Step -2 From -10     gt    -10  -12  -14  -16  -18      Also works with for  of loop for  i of new Range 5  -2  10   console log i      10 8 6 4 2  As Generators Only const Range   function   total   0  step   1  from   0      for  let i   0  i  lt  total  yield from   i     step         Array from Range 5  -2  -10        gt    -10  -12  -14  -16  -18       Range 5  -2  -10       Five Elements With Step -2 From -10     gt    -10  -12  -14  -16  -18      Also works with for  of loop for  i of Range 5  -2  10   console log i      10 8 6 4 2     Lazy loaded way const number0toInf   Range Infinity   number0toInf next   value      gt  0 number0toInf next   value      gt  1         From-To with steps delta using iterators class Range2     constructor to   0  step   1  from   0        this Symbol iterator    function             let i   0          length   Math floor  to - from    step    1        while  i  lt  length  yield from   i     step                   new Range2 5       First 5 Whole Numbers     gt   0  1  2  3  4  5       new Range2 5  2       From 0 to 5 with step 2     gt    0  2  4       new Range2 5  -2  10       From 10 to 5 with step -2     gt    10  8  6   using Generators const Range2   function   to   0  step   1  from   0      let i   0      length   Math floor  to - from    step    1    while  i  lt  length  yield from   i     step          Range2 5  -2  10       From 10 to 5 with step -2     gt    10  8  6   let even4to10   Range2 10  2  4   even4to10 next   value      gt  4 even4to10 next   value      gt  6 even4to10 next   value      gt  8 even4to10 next   value      gt  10 even4to10 next   value      gt  undefined  For Typescript class  Array lt T gt  extends Array lt T gt      static range from  number  to  number  step  number   number         return Array from Array Math floor  to - from    step    1   map         v  k    gt  from   k   step               Array range 0  9  1

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I found this old thread because I was wondering about the same myself  but I guess none of the answers here were easier than your original example as Kokodoko commented  haha   I ended up using this method myself   var foo       while  foo length  lt  N      foo push  foo length   1      Which is at least slightly faster to type out than a regular for-loop  and hopefully not error-prone  though it might be more expensive computational-wise    Can even do something like   var foo      while  foo length  lt  N      foo push  foo length 4   1      to fill the array with 1-4 multiple times in sequential order  Or use this method to fill the array with a single item  though I guess in that case it might be faster to just use Array N  fill x

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for var i a  i 0  i lt 10 a i    i     a    1  2  3  4  5  6  7  8  9  10

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If you happen to be using d3 js in your app as I am  D3 provides a helper function that does this for you   So to get an array from 0 to 4  it s as easy as   d3 range 5   0  1  2  3  4    and to get an array from 1 to 5  as you were requesting   d3 range 1  5 1   1  2  3  4  5    Check out this tutorial for more info

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Based on high voted answer and its high voted comment   const range    from  to    gt      Array to   1  keys    slice from       usage let test       test   range 5  10   console log test      output    5  6  7  8  9  10

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Try this  const foo   numberOfItems  gt      Array numberOfItems  keys    map i   gt  i 1

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In ES6 using Array from   and keys   methods  Array from Array 10  keys        gt   0  1  2  3  4  5  6  7  8  9   Shorter version using spread operator      Array 10  keys        gt   0  1  2  3  4  5  6  7  8  9   Start from 1 by passing map function to Array from    with an object with a length property  Array from  length  10       i    gt  i   1      gt   1  2  3  4  5  6  7  8  9  10

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function range start  end        var foo           for  var i   start  i  lt   end  i              foo push i             return foo      Then called by  var foo   range 1  5     There is no built-in way to do this in Javascript  but it s a perfectly valid utility function to create if you need to do it more than once   Edit  In my opinion  the following is a better range function  Maybe just because I m biased by LINQ  but I think it s more useful in more cases  Your mileage may vary   function range start  count        if arguments length    1            count   start          start   0             var foo           for  var i   0  i  lt  count  i              foo push start   i             return foo

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Well  simple but important question  Functional JS definitely lacks a generic unfold method under the Array object since we may need to create an array of numeric items not only simple  1 2 3     111  but a series resulting from a function  may be like x   gt  x 2 instead of x   gt  x  Currently  to perform this job we have to rely on the Array prototype map   method  However in order to use Array prototype map   we need to know the size of the array in advance  Well still   if we don t know the size  then we can utilize Array prototype reduce   but Array prototype reduce   is intended for reducing  folding  not unfolding right     So obviously we need an Array unfold   tool in functional JS  This is something that we can simply implement ourselves just like   Array unfold   function p f t s     var res          runner   v   gt   p v res length-1 res          res push f v   runner t v    res     return runner s        Arrays unfold p f t v  takes 4 arguments    p This is a function which defines where to stop  The p function takes 3 arguments like many array functors do  The value  the index and the currently resulting array  It shall return a Boolean value  When it returns a true the recursive iteration stops  f This is a function to return the next items functional value  t This is a function to return the next argument to feed to f in the next turn  s Is the seed value that will be used to calculate the comfortable seat of index 0 by f    So if we intend to create an array filled with a series like 1 4 9 16 25   n 2 we can simply do like    x000D   x000D  Array unfold   function p f t s   x000D    var res       x000D     runner   v   gt   p v res length-1 res          res push f v   runner t v    res   x000D    return runner s   x000D     x000D   x000D  var myArr   Array unfold    i    gt  i  gt   9  x   gt  Math pow x 2   x   gt  x 1  1   x000D  console log myArr   x000D   x000D   x000D

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The following function returns an array populated with numbers   var createArrayOfNumbers   function  n        return Array apply null  new Array n   map function  empty  index            return index               Note that an array created with the array constructor consists of holes  so it cannot be traversed with array functions like map  Hence using the Array apply function

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Final Summary report    Drrruummm Rolll -  This is the shortest code to generate an Array of size N  here 10  without using ES6  Cocco s version above is close but not the shortest    function n  for a    n-- a n  n 1  return a   10    But the undisputed winner of this Code golf competition to solve a particular problem in the fewest bytes of source code  is Niko Ruotsalainen   Using Array Constructor and ES6 spread operator    Most of the ES6 syntax is valid typeScript  but following is not  So be judicious while using it        Array 10  keys

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You can use Array fill and map from Es6  just like some few people suggested in the answers they gave for this question  Below are some few examples    Example-One  Array 10  fill 0  map  e i   gt i 1   Result-One   1  2  3  4  5  6  7  8  9  10   Example-Two  Array 100 10  fill 0  map  e i   gt  i 10  10   Result-Two  10  20  30  40  50  60  70  80  90  100     I prefer this because I find it straight forward and easier

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For small ranges a slice is nice  N is only known at runtime  so    0  1  2  3  4  5  slice 0  N 1

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Fast This solution is probably fastest it is inspired by lodash   range function  but my is simpler and faster   x000D   x000D  let N 10  i 0  a Array N    while i lt N  a i    i     console log a   x000D   x000D   x000D   Performance advantages over current  2020 12 11  existing answers based on while for  memory is allocated once at the beginning by a Array N  increasing index i   is used -  which looks is about 30  faster than decreasing index i--  probably because CPU cache memory faster in forward direction   Speed tests with more than 20 other solutions was conducted in this answer

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ES6 solution using recursion  Different than all other solutions  const range    n  A         gt   n     1     n     A    range n - 1   n     A      console log range 5

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The question was for alternatives to this technique but I wanted to share the faster way of doing this   It s nearly identical to the code in the question but it allocates memory instead of using push   function range n        let a   Array n       for  let i   0  i  lt  n  a i      i       return a

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Using ES6  const generateArray   n   gt      Array n   map     index    gt  index   1

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the new way to filling Array is    x000D   x000D  const array       Array 5  keys    x000D  console log array  x000D   x000D   x000D    result will be   0  1  2  3  4

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It seems the only flavor not currently in this rather complete list of answers is one featuring a generator  so to remedy that   const gen   N   gt       function    let i 0 while i lt N yield i          which can be used thus   gen 4      0 1 2 3    The nice thing about this is you don t just have to increment    To take inspiration from the answer  igor-shubin gave  you could create an array of randoms very easily   const gen   N   gt       function    let i 0    while i   lt N  yield Math random           And rather than something lengthy operationally expensive like   const slow   N   gt  new Array N  join   split      map  e i   gt i 5      0 5 10 15        you could instead do   const fast   N   gt       function    let i 0 while i   lt N yield i 5

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Performance Today 2020 12 11 I perform tests on MacOs HighSierra 10 13 6 on Chrome v87  Safari v13 1 2 and Firefox v83 for chosen solutions  Results For all browsers  solution O  based on while  is fastest  except Firefox for big N - but it s fast there  solution T is fastest on Firefox for big N solutions M P are fast for small N solution V  lodash  is fast for big N solution W X are slow for small N solution F is slow   Details I perform 2 tests cases   for small N   10 - you can run it HERE for big N   1000000 - you can run it HERE  Below snippet presents all tested solutions A B C D E F G H I J K L M N O P Q R S T U V W X  x000D   x000D  function A N      return Array from  length  N       i    gt  i   1     function B N      return Array N  fill   map     i    gt  i 1      function C N      return Array N  join   split      map     i    gt  i 1       function D N      return Array from Array N       i    gt  i 1     function E N      return Array from   length  N        i    gt  i 1     function F N      return Array from  length N   Number call  i   gt  i   1     function G N      return  Array N      split      map    i   gt  i 1     function H N      return      Array N  keys     map  i   gt  i 1      function I N      return     Array N  keys    map x   gt  x   1      function J N      return     Array N 1  keys    slice 1     function K N      return     Array N  keys    map x   gt    x      function L N      let arr   arr      Array N 1  keys      shift      return arr     function M N      var arr         var i   0     while  N--  arr push   i      return arr      function N N      var a    b N while b-- a b  b 1    return a     function O N      var a Array N  b 0    while b lt N  a b    b    return a     function P N      var foo         for  var i   1  i  lt   N  i    foo push i     return foo     function Q N      for var a    b N b-- a b  b 1     return a     function R N      for var i a  i 0  i lt N a i    i     return a     function S N        let foo x      for foo  x N   x  foo x-1  x--     return foo     function T N      return new Uint8Array N  map  item  i    gt  i   1      function U N      return     repeat 5  split     map     i    gt  i   1      function V N      return   range 1  N 1      function W N      return      function    let i 0 while i lt N yield   i         function X N      function sequence max  step   1        return          Symbol iterator   function               for  let i   1  i  lt   max  i    step  yield i                      return     sequence N         A B C D E F G H I J K L M N O P Q R S T U V W X  forEach f  gt      console log    f name    f 5         x000D   lt script src  https   cdnjs cloudflare com ajax libs lodash js 4 17 20 lodash min js  integrity  sha512-90vH1Z83AJY9DmlWa8WkjkV79yfS2n2Oxhsi2dZbIv0nC4E6m5AbH8Nh156kkM7JePmqD6tcZsfad1ueoaovww    crossorigin  anonymous  gt   lt  script gt     This shippet only presents functions used in performance tests - it not perform tests itself  x000D   x000D   x000D   And here are example results for chrome

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You can use this   new Array   any number which you want         join   split           map function item  index   return   index      for example  new Array 10       join   split           map function item  index   return   index      will create following array    1  2  3  4  5  6  7  8  9  10

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Here is the summary  run in console       setup  var n   10000000  function  rangeIter a  b        for  let i   a  i  lt   b    i  yield i    function range n         let a          for    n--  a n    n       return a    function sequence max  step   1        return            Symbol iterator   function                   for  let i   1  i  lt   max  i    step  yield i                    var t0  t1  arr     tests t0   performance now    arr   Array from   length  n     a  i    gt  1  t1   performance now    console log  Array from   length  n     a  i    gt  1  Took      t1 - t0      milliseconds      t0   performance now    arr   range n   t1   performance now    console log  range n  Took      t1 - t0      milliseconds      t0   performance now    arr   Array from rangeIter 0  n    t1   performance now    console log  Array from rangeIter 0  n   Took      t1 - t0      milliseconds      t0   performance now    arr       rangeIter 0  n    t1   performance now    console log      rangeIter 0  n   Took      t1 - t0      milliseconds      t0   performance now    arr   Array from sequence n    t1   performance now    console log  Array from sequence n   Took      t1 - t0      milliseconds      t0   performance now    arr       sequence n    t1   performance now    console log      sequence n   Took      t1 - t0      milliseconds      t0   performance now    arr   Array n  fill 0  map Number call  Number   t1   performance now    console log  Array n  fill 0  map Number call  Number  Took      t1 - t0      milliseconds      t0   performance now    arr   Array from Array n  keys     t1   performance now    console log  Array from Array n  keys    Took      t1 - t0      milliseconds      t0   performance now    arr       Array n  keys     t1   performance now    console log      Array n  keys    Took      t1 - t0      milliseconds       The fastest is Array n  fill 0  map Number call  Number   2nd is     Array n  keys     But     rangeIter  way is quite handy  can be inlined   fast and more powerful

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Arrays innately manage their lengths   As they are traversed  their indexes can be held in memory and referenced at that point   If a random index needs to be known  the indexOf method can be used    This said  for your needs you may just want to declare an array of a certain size     var foo   new Array N        where N is a positive integer     this will create an array of size  N  primarily for memory allocation      but does not create any defined values     foo length                                   size of Array    foo  Math floor foo length 2       value     places value in the middle of the array        ES6  Spread  Making use of the spread operator       and keys method  enables you to create a temporary array of size N to produce the indexes  and then a new array that can be assigned to your variable   var foo        Array N  keys        Fill Map  You can first create the size of the array you need  fill it with undefined and then create a new array using map  which sets each element to the index   var foo   Array N  fill   map  v i   gt i     Array from  This should be initializing to length of size N and populating the array in one pass   Array from   length  N     v  i    gt  i        In lieu of the comments and confusion  if you really wanted to capture the values from 1  N in the above examples  there are a couple options    if the index is available  you can simply increment it by one  e g     i     in cases where index is not used -- and possibly a more efficient way -- is to create your array but make N represent N 1  then shift off the front      So if you desire 100 numbers     let arr   arr      Array 101  keys      shift

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Use the very popular Underscore   range method       range  start   stop   step      range 10        gt   0  1  2  3  4  5  6  7  8  9    range 1  11        gt   1  2  3  4  5  6  7  8  9  10    range 0  30  5        gt   0  5  10  15  20  25    range 0  -10  -1         gt   0  -1  -2  -3  -4  -5  -6  -7  -8  -9    range 0        gt

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var foo   Array from Array N    v  i    gt  i   1

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Just for fun  I wanted to build off of Ian Henry s answer   Of course var array   new Array N   will give you an array of size N  but the keys and values will be identical     then to shorten the array to size M  use array length   M     but for some added functionality try   function range            This function takes optional arguments         start  end  increment           start may be larger or smaller than end        Example   range null  null  2        var array          Create empty array           Get arguments or set default values      var start    arguments 0    arguments 0    0       var end      arguments 1    arguments 1    9            If start    end return array of size 1     if  start    end    array push start   return array        var inc      arguments 2    Math abs arguments 2     1        inc     start  gt  end   -1   1      Figure out which direction to increment            Loop ending condition depends on relative sizes of start and end     for  var i   start   start  lt  end   i  lt   end   i  gt   end    i    inc          array push i        return array     var foo   range 1  -100  8 5   for var i 0 i lt foo length i       document write foo i      is item       i 1      of     foo length     lt br  gt           Output of the above      1 is item  1 of 12   -7 5 is item  2 of 12   -16 is item  3 of 12   -24 5 is item  4 of 12   -33 is item  5 of 12   -41 5 is item  6 of 12   -50 is item  7 of 12   -58 5 is item  8 of 12   -67 is item  9 of 12   -75 5 is item  10 of 12   -84 is item  11 of 12   -92 5 is item  12 of 12     jsFiddle example  This function makes use of the automatically generated arguments array   The function creates an array filled with values beginning at start and ending at end with increments of size increment  where  range start  end  increment     Each value has a default and the sign of the increment doesn t matter  since the direction of incrementation depends on the relative sizes of start and end

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to get array with n random numbers between min  max  not unique though   function callItWhatYouWant n  min  max        return Array apply null   length  n   map Function call  function   return Math floor Math random    max-min 1  min

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x000D   x000D     A solution where you do not allocate a N sized array  ES6  with some flow annotation   x000D  function  zeroToN N      number         Generator lt number  void  empty gt       x000D    for  let n   0  n  lt   N  n    1  yield n  x000D    x000D   x000D     With this generation  you can have your array x000D  console log     zeroToN 10-1    x000D   x000D     but let s define a helper iterator function x000D  function mapIterator iterator  mapping    x000D    const arr       x000D    for  let result   iterator next     result done  result   iterator next      x000D      arr push mapping result value    x000D      x000D    return arr  x000D    x000D   x000D     now you have a map function  without allocating that 0   N-1 array x000D   x000D  console log mapIterator zeroToN 10-1   n   gt  n n    x000D   x000D   x000D

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Try adding an iterator to Number s prototype   Number prototype Symbol iterator    function        let i   0    while i  lt  this  yield i      return      Now that numbers are iterable  simply pass a number to Array from  Array from 10     0  1  2  3  4  5  6  7  8  9    or anywhere else an iterable is required  like for   of loops   for const number of 10  console log number    logs 0 through 9 sequentially   It s somewhat convoluted  but also cool

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Answered in Feb 2021 Very simple and easy to generate exactly 1 - N  x000D   x000D  const n   10  const       result    Array n   1  keys     console log  Result    result   x000D   x000D   x000D

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Multiple ways using ES6  Using spread operator       and keys method       Array N  keys     map  i   gt  i 1     Fill Map  Array N  fill   map     i    gt  i 1     Array from  Array from Array N       i    gt  i 1    Array from and   length  N   hack  Array from   length  N        i    gt  i 1    Note about generalised form  All the forms above can produce arrays initialised to pretty much any desired values by changing i 1 to expression required  e g  i 2  -i  1 i 2  i 2 and etc   If expression can be expressed by some function f then the first form becomes simply       Array N  keys     map f    Examples   Array from  length  5    v  k    gt  k 1        1 2 3 4 5    Since the array is initialized with undefined on each position  the value of v  will be undefined  Example showcasing all the forms   x000D   x000D  let demo   N    gt    x000D    console log  x000D           Array N  keys     map   i    gt  i 1   x000D      Array N  fill   map     i    gt  i 1    x000D      Array from Array N       i    gt  i 1   x000D      Array from   length  N        i    gt  i 1  x000D      x000D    x000D   x000D  demo 5  x000D   x000D   x000D    More generic example with custom initialiser function f i e        Array N  keys     map  i    gt  f i     or even simpler       Array N  keys     map f     x000D   x000D  let demo   N f    gt    x000D    console log  x000D           Array N  keys     map f   x000D      Array N  fill   map     i    gt  f i     x000D      Array from Array N       i    gt  f i    x000D      Array from   length  N        i    gt  f i   x000D      x000D    x000D   x000D  demo 5  i  gt 2 i 1  x000D   x000D   x000D

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There is another way in ES6  using Array from which takes 2 arguments  the first is an arrayLike  in this case an object with length property   and the second is a mapping function  in this case we map the item to its index   Array from  length 10    v i    gt  i    this is shorter and can be used for other sequences like generating even numbers  Array from  length 10    v i    gt  i 2    Also this has better performance than most other ways because it only loops once through the array  Check the snippit for some comparisons   x000D   x000D     open the dev console to see results x000D   x000D  count   100000 x000D   x000D  console time  from object   x000D  for  let i   0  i lt count  i      x000D    range   Array from  length 10    v i    gt  i   x000D    x000D  console timeEnd  from object   x000D   x000D  console time  from keys   x000D  for  let i  0  i lt count  i      x000D    range   Array from Array 10  keys    x000D    x000D  console timeEnd  from keys   x000D   x000D  console time  apply   x000D  for  let i   0  i lt count  i      x000D    range   Array apply null    length  10    map function element  index    return index     x000D    x000D  console timeEnd  apply   x000D   x000D   x000D

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If I get what you are after  you want an array of numbers 1  n that you can later loop through   If this is all you need  can you do this instead   var foo   new Array 45      create an empty array with length 45   then when you want to use it     un-optimized  just for example   for var i   0  i  lt  foo length  i       document write  Item       i   1      of     foo length     lt br  gt          e g  if you don t need to store anything in the array  you just need a container of the right length that you can iterate over    this might be easier   See it in action here  http   jsfiddle net 3kcvm

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I would do it this way using    Array N  keys    x000D   x000D  var foo       Array 5  keys    map foo   gt  foo   1   console log foo  x000D   x000D   x000D

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As there are a lot of good answers this might be an option as well  you can also create a function with the below and it will work for any combination of numbers  const start   10  const end   30      const difference   Math abs start-end   const rangeArray   new Array difference   1  fill undefined  map  val  key    gt        return start  gt  end   start - key   start   key

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x000D   x000D  Array    Array 9   map     i    gt  i   x000D   x000D  console log Array    Array 9   map     i    gt  i   x000D   x000D   x000D

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Array prototype fill    a   Object keys     fill call  length 7          map Number  a pop    console debug a     0  1  2  3  4  5  6

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There is small function  it allow to use construction like  1  2  range 3  4  -   1  2  3  4  also it works with negative params  Enjoy   Array prototype range   function from  to       var range     to   from   Math abs to - from    1  increase   from  lt  to     var tmp   Array apply this    length   range   map function                    return  increase  from     from--           Number       return this concat tmp

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Just another ES6 version   By making use of Array from second optional argument      Array from arrayLike   mapFn   thisArg      We can build the numbered array from the empty Array 10  positions   Array from Array 10       i    gt  i       x000D   x000D  var arr   Array from Array 10       i    gt  i   x000D  document write arr   x000D   x000D   x000D

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function arrGen n      var a   Array n    while  n--  a n    n   return a      arrGen 10    gt   0  1  2  3  4  5  6  7  8  9

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This question has a lot of complicated answers  but a simple one-liner       Array 255  keys    map x   gt  x   1      Also  although the above is short  and neat  to write  I think the following is a bit faster   for a max length of    127  Int8   255  Uint8    32 767  Int16   65 535  Uint16   2 147 483 647  Int32    4 294 967 295  Uint32    based on the max integer values   also here s more on Typed Arrays     new Uint8Array 255   map    i    gt  i   1     Although this solution is also not so ideal  because it creates two arrays  and uses the extra variable declaration      not sure any way to get around that using this method   I think the following solution is the absolute fastest possible way to do this   for var i   0  arr   new Uint8Array 255   i  lt  arr length  i    arr i    i   1    Anytime after this statement is made  you can simple use the variable  arr  in the current scope   If you want to make a simple function out of it  with some basic verification      x000D   x000D  function range min  max    x000D      min   min  amp  amp  min constructor    Number   min   0  x000D        max  amp  amp  max constructor    Number  amp  amp  max  gt  min   amp  amp     boolean statements can also be used with void return types  like a one-line if statement  x000D            max   min   amp   min   0       if there is a  max  argument specified  then first check if its a number and if its graeter than min  if so  stay the same  if not  then consider it as if there is no  max  in the first place  and  max  becomes  min   and min becomes 0 by default  x000D   x000D      for var i   0  arr   new   x000D          max  lt  128   Int8Array    x000D          max  lt  256   Uint8Array   x000D          max  lt  32768   Int16Array    x000D          max  lt  65536   Uint16Array   x000D          max  lt  2147483648   Int32Array   x000D          max  lt  4294967296   Uint32Array    x000D          Array x000D        max - min   i  lt  arr length  i    arr i    i   min  x000D      return arr  x000D    x000D   x000D   x000D   x000D    and you can loop through it easily using array methods if you want x000D  range 1 11  forEach x   gt  console log x    x000D   x000D    or if you re used to pythons  for   in  you can do a similar thing with  for   of  if you want the individual values  x000D  for i of range 2020 2025   console log i   x000D   x000D    or if you really want to use  for  in   you can  but then you will only be accessing the keys  x000D   x000D  for k in range 25 30   console log k   x000D   x000D  console log  x000D      range 1 128  constructor name  x000D      range 200  constructor name  x000D      range 400 900  constructor name  x000D      range 33333  constructor name  x000D      range 823  100000  constructor name  x000D      range 10 4     when the  min  argument is greater than the  max   then it just considers it as if there is no  max   and the new max becomes  min   and  min  becomes 0  as if  max  was never even written x000D     x000D   x000D   x000D      so  with the above function  the above super-slow  simple one-liner  becomes the super-fast  even-shorter   range 1 14000

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ES5 version  inefficient  but perhaps the shortest one that s an expression  not some statement where a variable is populated with eg  a for loop     Array N      split      map function d i  return i

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This is probably the fastest way to generate an array of numbers  Shortest  var a    b N while b-- a b  b 1    Inline  var arr  function a b  while a-- b a  a return b   10        arr  0 1 2 3 4 5 6 7 8 9    If you want to start from 1  var arr  function a b  while a-- b a  a 1 return b   10        arr  1 2 3 4 5 6 7 8 9 10    Want a function   function range a b c  c    while a-- c a  a b return c     length start placeholder var arr range 10 5     arr  5 6 7 8 9 10 11 12 13 14    WHY    while is the fastest loop Direct setting is faster than push    is faster than new Array 10  it s short    look the first code  then look at all other functions in here    If you like can t live without for  for var a    b 7 b gt 0 a --b  b 1     a  1 2 3 4 5 6 7    or  for var a    b 7 b-- a b  b 1     a  1 2 3 4 5 6 7

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Using new Array methods and   gt  function syntax from ES6 standard  only Firefox at the time of writing    By filling holes with undefined    Array N  fill   map     i    gt  i   1     Array from turns  holes  into undefined so Array map works as expected   Array from Array 5   map     i    gt  i   1

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Improvising on the above   var range   function  n      return Array n  join   split      map function e  i    return i            one can get the following options   1  Array init to value v  var arrayInitTo   function  n v      return Array n  join   split      map function     return v            2  get a reversed range   var rangeRev   function  n      return Array n  join   split      map function     return n--

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Using ES2015 ES6 spread operator      Array 10   map     i    gt  i   1     x000D   x000D  console log     Array 10   map     i    gt  i   1   x000D   x000D   x000D

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You can do so   var N   10   Array apply null   length  N   map Number call  Number       result    0  1  2  3  4  5  6  7  8  9    or with random values   Array apply null   length  N   map Function call  Math random       result   0 7082694901619107  0 9572225909214467  0 8586748542729765    0 8653848143294454  0 008339877473190427  0 9911756622605026  0 8133423360995948  0 8377588465809822  0 5577575915958732  0 16363654541783035    Explanation  First  note that Number call undefined  N  is equivalent to Number N   which just returns N   We ll use that fact later   Array apply null   undefined  undefined  undefined   is equivalent to Array undefined  undefined  undefined   which produces a three-element array and assigns undefined to each element   How can you generalize that to N elements   Consider how Array   works  which goes something like this   function Array         if   arguments length    1  amp  amp            number      typeof arguments 0   amp  amp           arguments 0   gt   0  amp  amp  arguments  amp  amp           arguments 0   lt  1  lt  lt  32             return              array of length arguments 0   generated by native code           var a           for  var i   0  i  lt  arguments length  i              a push arguments i              return a      Since ECMAScript 5  Function prototype apply thisArg  argsArray  also accepts a duck-typed array-like object as its second parameter   If we invoke Array apply null    length  N     then it will execute  function Array         var a           for  var i   0  i  lt     arguments length      N  i              a push    arguments i       undefined             return a      Now we have an N-element array  with each element set to undefined   When we call  map callback  thisArg  on it  each element will be set to the result of callback call thisArg  element  index  array    Therefore   undefined  undefined       undefined  map Number call  Number  would map each element to  Number call  call Number  undefined  index  array   which is the same as Number call undefined  index  array   which  as we observed earlier  evaluates to index   That completes the array whose elements are the same as their index   Why go through the trouble of Array apply null   length  N   instead of just Array N    After all  both expressions would result an an N-element array of undefined elements   The difference is that in the former expression  each element is explicitly set to undefined  whereas in the latter  each element was never set   According to the documentation of  map        callback is invoked only for indexes of the array which have assigned values  it is not invoked for indexes which have been deleted or which have never been assigned values    Therefore  Array N  is insufficient  Array N  map Number call  Number  would result in an uninitialized array of length N   Compatibility  Since this technique relies on behaviour of Function prototype apply   specified in ECMAScript 5  it will not work in pre-ECMAScript 5 browsers such as Chrome 14 and Internet Explorer 9

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If you are using lodash  you can use   range        range  start 0   end   step 1        Creates an array of numbers    positive and or negative  progressing from start up to  but not   including  end  A step of -1 is used if a negative start is specified   without an end or step  If end is not specified  it s set to start   with start then set to 0    Examples     range 4         0  1  2  3     range -4         0  -1  -2  -3     range 1  5         1  2  3  4     range 0  20  5         0  5  10  15     range 0  -4  -1         0  -1  -2  -3     range 1  4  0         1  1  1     range 0

[javascript] How to create an array containing 1...N

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