How to generate range of numbers from 0 to n in ES2015 only

Question

I have always found the range function missing from JavaScript as it is available in python and others  Is there any concise way to generate range of numbers in ES2015    EDIT  MY question is different from the mentioned duplicate as it is specific to ES2015 and not ECMASCRIPT-5  Also I need the range to be starting from 0 and not specific starting number  though it would be good if that is there

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Range with step ES6  that works similar to python list range start  stop   step      const range    start  stop  step   1    gt      return     Array stop - start  keys         filter i   gt    i   Math round step         map v   gt  start   v      Examples   range 0  8      0  1  2  3  4  5  6  7  range 4  9      4  5  6  7  8  range 4  9  2      4  6  8   range 4  9  3      4  7

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I also found one more intuitive way using Array from   const range   n   gt  Array from  length  n    value  key    gt  key    Now this range function will return all the numbers starting from 0 to n-1   A modified version of the range to support start and end is   const range    start  end    gt  Array from  length   end - start     v  k    gt  k   start     EDIT As suggested by  marco6  you can put this as a static method if it suits your use case  Array range    start  end    gt  Array from  length   end - start     v  k    gt  k   start     and use it as  Array range 3  9

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To support delta  const range    start  end  delta    gt      return Array from       length   end - start    delta    v  k    gt   k   delta    start

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You can use the spread operator on the keys of a freshly created array       Array n  keys     or  Array from Array n  keys     The Array from   syntax is necessary if working with TypeScript

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You can use a generator function  which creates the range lazily only when needed    x000D   x000D  function  range x  y    x000D    while  true    x000D      if  x  lt   y  x000D        yield x    x000D   x000D      else x000D        return null  x000D      x000D    x000D   x000D  const infiniteRange   x   gt  x000D    range x  Infinity   x000D     x000D  console log  x000D    Array from range 1  10       1 2 3 4 5 6 7 8 9 10  x000D     x000D   x000D  console log  x000D    infiniteRange 1000000  next   x000D     x000D   x000D   x000D    You can use a higher order generator function to map over the range generator    x000D   x000D  function  range x  y    x000D    while  true    x000D      if  x  lt   y  x000D        yield x    x000D   x000D      else x000D        return null  x000D      x000D    x000D   x000D  const genMap   f   gt  gx   gt  function      args    x000D    for  const x of gx    args   x000D      yield f x   x000D     x000D   x000D  const dbl   n   gt  n   2  x000D   x000D  console log  x000D    Array from  x000D      genMap dbl   range   1  10       2 4 6 8 10 12 14 16 18 20  x000D     x000D   x000D   x000D    If you are fearless you can even generalize the generator approach to address a much wider range  pun intended     x000D   x000D  const rangeBy    p  f    gt  function  rangeBy x    x000D    while  true    x000D      if  p x     x000D        yield x  x000D        x   f x   x000D        x000D   x000D      else x000D        return null  x000D      x000D     x000D   x000D  const lte   y   gt  x   gt  x  lt   y  x000D   x000D  const inc   n   gt  n   1  x000D   x000D  const dbl   n   gt  n   2  x000D   x000D  console log  x000D    Array from rangeBy lte 10   inc   1       1 2 3 4 5 6 7 8 9 10  x000D     x000D   x000D  console log  x000D    Array from rangeBy lte 256   dbl   2       2 4 8 16 32 64 128 256  x000D     x000D   x000D   x000D    Keep in mind that generators iterators are inherently stateful that is  there is an implicit state change with each invocation of next  State is a mixed blessing

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A lot of these solutions build on instantiating real Array objects  which can get the job done for a lot of cases but can t support cases like range Infinity   You could use a simple generator to avoid these problems and support infinite sequences   function  range  start  end  step   1      if  end     undefined    end  start     start  0     for  let n   start  n  lt  end  n    step   yield n      Examples   Array from range 10             0  1  2  3  4  5  6  7  8  9   Array from range 10  20         10  11  12  13  14  15  16  17  18  19    i   range 10  Infinity   i next         value  10  done  false   i next         value  11  done  false   i next         value  12  done  false   i next         value  13  done  false   i next         value  14  done  false

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For numbers 0 to 5      Array 5  keys       gt   0  1  2  3  4

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So  in this case  it would be nice if Number object would behave like an Array object with the spread operator   For instance Array object used with the spread operator   let foo    0 1 2 3   console log    foo     returns 0 1 2 3   It works like this because Array object has a built-in iterator  In our case  we need a Number object to have a similar functionality       3    should return  0 1 2 3    To do that we can simply create Number iterator for that purpose   Number prototype Symbol iterator    function          for let i   0  i  lt   this  i           yield i      Now it is possible to create ranges from 0 to N with the spread operator          N     now returns 0     N array    http   jsfiddle net 01e4xdv5 4   Cheers

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With Delta Step smallest and one-liner     Array N   map     i    gt  from   i   step    Examples and other alternatives     Array 10   map     i    gt  4   i   2       gt   4  6  8  10  12  14  16  18  20  22   Array from Array 10   map     i    gt  4   i   2       gt   4  6  8  10  12  14  16  18  20  22   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     i    gt  4   i   2       gt   4  6  8  10  12  14  16  18  20  22   Array 10  fill   map     i    gt  4   i   -2       gt   4  2  0  -2  -4  -6  -8  -10  -12  -14   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 interface  Iterable extends Iterable lt    gt      length  number     class  Array lt T gt  extends Array lt T gt      static range from  number  to  number  step  number   number         return Array from         lt  Iterable gt   length  Math floor  to - from    step    1           v  k    gt  from   k   step               Array range 0  9  1       gt   0  1  2  3  4  5  6  7  8  9    Update class  Array lt T gt  extends Array lt T gt      static range from  number  to  number  step  number   number         return     Array Math floor  to - from    step    1   map         v  k    gt  from   k   step               Array range 0  9  1    Edit 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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Here s another variation that doesn t use Array   let range    n  l     delta 1    gt      if  n  lt  0         return l        else       l unshift n      return range n - delta  l

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const keys   Array n  keys        Array from keys   forEach callback     in Typescript

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This function will return an integer sequence   const integerRange    start  end  n   start  arr         gt     n     end        arr  n        integerRange start  end  start  lt  end   n   1   n - 1      arr  n       gt  integerRange 1  1   lt - Array   1      gt  integerRange 1  3   lt - Array 3    1  2  3      gt  integerRange 3  -3   lt - Array 7    3  2  1  0  -1  -2  -3

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How about just mapping      Array n  map  value  index        is 80  of the way there  But for some odd reason it does not work  But there is a workaround  Array n  map  v i    gt  i     does not work Array n  fill   map  v i    gt  i     does dork  For a range Array end-start 1  fill   map  v i    gt  i   start     gives you a range  Odd  these two iterators return the same result  Array end-start 1  entries   and Array end-start 1  fill   entries

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Generators now allow you to generate the number sequence lazily and using less memory for large ranges    While the question specifically states ES2015  I expect a lot of Typescript users will end up here and the conversion to ES is straightforward     function range end  number   IterableIterator lt number gt      tslint disable-next-line unified-signatures function range begin  number  end  number   IterableIterator lt number gt    function  range begin  number  end  number   NaN   IterableIterator lt number gt        let num   0      if  isNaN end             end   begin        else           num   begin            while  num  lt  end            yield num              The first two function declarations are just to provide more informative completion suggestions in your IDE

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You can also do it with a one liner with step support like this one     from  to  step    gt    add  arr  v    gt  add arr  v  add    arr  v  add    gt  v  lt  to   add arr concat  v    v   step  add    arr      from   0  10  1   The result is  0  1  2  3  4  5  6  7  8  9

[javascript] How to generate range of numbers from 0 to n in ES2015 only?

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