Most efficient way to create a zero filled JavaScript array

Question

What is the most efficient way to create an arbitrary length zero filled array in JavaScript

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What about new Array 51  join  0   split

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function makeArrayOf value  length      var arr       i   length    while  i--        arr i    value        return arr     makeArrayOf 0  5       0  0  0  0  0   makeArrayOf  x   3        x    x    x     Note that while is usually more efficient than for-in  forEach  etc

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Another nice option found here http   www 2ality com 2013 11 initializing-arrays html  function fillArrayWithNumbers n      var arr   Array apply null  Array n      return arr map function  x  i    return i

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I was testing out the great answer by T J  Crowder  and came up with a recursive merge based on the concat solution that outperforms any in his tests in Chrome  i didn t test other browsers    function makeRec len  acc        if  acc    null  acc           if  len  lt   1  return acc      var b   makeRec len  gt  gt  1   0        b   b concat b       if  len  amp  1  b   b concat  0        return b       call the method with makeRec 29

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In short Fastest solution let a   new Array n   for  let i 0  i lt n    i  a i    0  Shortest  handy  solution  3x slower for small arrays  slightly slower for big  slowest on Firefox   Array n  fill 0   Details Today 2020 06 09 I perform tests on macOS High Sierra 10 13 6 on browsers Chrome 83 0  Firefox 77 0  and Safari 13 1  I test chosen solutions for two test cases  small array - with 10 elements - you can perform test HERE big arrays - with 1M elements - you can perform test HERE  Conclusions  solution based on new Array n  for  N  is fastest solution for small arrays and big arrays  except Chrome but still very fast there  and it is recommended as fast cross-browser solution solution based on new Float32Array n   I  returns non typical array  e g  you cannot call push     on it  so I not compare its results with other solutions - however this solution is about 10-20x faster than other solutions for big arrays on all browsers solutions based on for  L M N O  are fast for small arrays solutions based on fill  B C  are fast on Chrome and Safari but surprisingly slowest on Firefox for big arrays  They are medium fast for small arrays solution based on Array apply  P  throws error for big arrays  x000D   x000D  function P n      return Array apply null  Array n   map Number prototype valueOf 0       try     P 1000000     catch e       console error e message     x000D   x000D   x000D     Code and example Below code presents solutions used in measurements  x000D   x000D  function A n      return     new Array n   fill 0      function B n      return new Array n  fill 0      function C n      return Array n  fill 0      function D n      return Array from  length  n        gt  0      function E n      return     new Array n   map x   gt  0         arrays with type  function F n      return Array from new Int32Array n       function G n      return Array from new Float32Array n       function H n      return Array from new Float64Array n       needs 2x more memory than float32    function I n      return new Float32Array n      this is not typical array    function J n      return    slice apply new Float32Array n          Based on for  function K n      let a         a length   n    let i   0    while  i  lt  n        a i    0      i          return a     function L n      let a     for let i 0  i lt n  i    a i  0    return a     function M n      let a     for let i 0  i lt n  i    a push 0     return a     function N n      let a   new Array n   for  let i 0  i lt n    i  a i    0    return a     function O n      let a   new Array n   for  let i n  i--   a i    0    return a        other  function P n      return Array apply null  Array n   map Number prototype valueOf 0      function Q n      return  0  repeat  n   split     map  parseFloat       function R n      return new Array n 1  join  0   split     map parseFloat         ---------    TEST    ---------   A B C D E F G H I J K L M N O P Q R  forEach f   gt      let a   f 10      console log    f name  length   a length   arr 0    a 0    arr 9    a 9         x000D  This snippets only present used codes x000D   x000D   x000D   Example results for Chrome

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I just use    var arr    10   for  var i 0  i lt  arr length arr i    i  i

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You can check if index exist or not exist  in order to append  1 to it   this way you don t need a zeros filled array   EXAMPLE   var current year   new Date   getFullYear    var ages array   new Array     for  var i in data        if data i   BirthDate      null  amp  amp  data i   BirthDate       0000-00-00             var birth   new Date data i   BirthDate             var birth year   birth getFullYear            var age   current year - birth year           if ages array age     null               ages array age    1           else              ages array age     1                      console log ages array

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x000D   x000D  let filled       x000D  filled length   10  x000D  filled fill 0   x000D   x000D  console log filled   x000D   x000D   x000D

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This concat version is much faster in my tests on Chrome  2013-03-21   About 200ms for 10 000 000 elements vs 675 for straight init   function filledArray len  value        if  len  lt   0  return         var result    value       while  result length  lt  len 2            result   result concat result             return result concat result slice 0  len-result length        Bonus  if you want to fill your array with Strings  this is a concise way to do it  not quite as fast as concat though    function filledArrayString len  value        return new Array len 1  join value  split

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As of ECMAScript2016  there is one clear choice for large arrays    Since this answer still shows up near the top on google searches  here s an answer for 2017   Here s a current jsbench with a few dozen popular methods  including many proposed up to now on this question  If you find a better method please add  fork and share   I want to note that there is no true most efficient way to create an arbitrary length zero filled array  You can optimize for speed  or for clarity and maintainability - either can be considered the more efficient choice depending on the needs of the project   When optimizing for speed  you want to  create the array using literal syntax  set the length  initialize iterating variable  and iterate through the array using a while loop  Here s an example    x000D   x000D  const arr       x000D  arr length   120000  x000D  let i   0  x000D  while  i  lt  120000    x000D    arr i    0  x000D    i    x000D    x000D   x000D   x000D    Another possible implementation would be    arr       length   n  let i   0  while  i  lt  n        arr i    0      i        But I strongly discourage using this second implantation in practice as it s less clear and doesn t allow you to maintain block scoping on your array variable   These are significantly faster than filling with a for loop  and about 90  faster than the standard method of   const arr   Array n  fill 0     But this fill method is still the most efficient choice for smaller arrays due to it s clarity  conciseness and maintainability  The performance difference likely won t kill you unless you re making a lot of arrays with lengths on the order of thousands or more   A few other important notes  Most style guides recommend you no longer use varwithout a very special reason when using ES6 or later  Use const for variables that won t be redefined and let for variables that will  The MDN and Airbnb s Style Guide are great places to go for more information on best practices  The questions wasn t about syntax  but it s important that people new to JS know about these new standards when searching through these reams of old and new answers

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using object notation  var x         zero filled  like     var x    0 0 0 0 0 0     filled with  undefined      var x   new Array 7     obj notation with zeros  var x       for  var i   0  i  lt  10  i    x i    0    As a side note  if you modify Array s prototype  both  var x   new Array      and  var y         will have those prototype modifications  At any rate  I wouldn t be overly concerned with the efficiency or speed of this operation  there are plenty of other things that you will likely be doing that are far more wasteful and expensive than instanciating an array of arbitrary length containing zeros

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Although this is an old thread  I wanted to add my 2 cents to it  Not sure how slow fast this is  but it s a quick one liner  Here is what I do   If I want to pre-fill with a number   Array apply null  Array 5   map Number prototype valueOf 0       0  0  0  0  0    If I want to pre-fill with a string   Array apply null  Array 3   map String prototype valueOf  hi        hi    hi    hi       Other answers have suggested   new Array 5 1  join  0   split          0    0    0    0    0     but if you want 0  the number  and not  0   zero inside a string   you can do   new Array 5 1  join  0   split     map parseFloat      0  0  0  0  0

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ES6 introduces Array prototype fill  It can be used like this   new Array len  fill 0     Not sure if it s fast  but I like it because it s short and self-describing   It s still not in IE  check compatibility   but there s a polyfill available

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By default Uint8Array  Uint16Array and Uint32Array classes keep zeros as its values  so you don t need any complex filling techniques  just do   var ary   new Uint8Array 10     all elements of array ary will be zeros by default

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x000D   x000D  const arr   Array from   length  10    fill 0  x000D   x000D   x000D

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The already mentioned ES 6 fill method takes care of this nicely  Most modern desktop browsers already support the required Array prototype methods as of today  Chromium  FF  Edge and Safari   1   You can look up details on MDN  A simple usage example is  a   new Array 10  fill 0     Given the current browser support you should be cautious to use this unless you are sure your audience uses modern Desktop browsers

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Anonymous function    function n    while n--  amp  amp  this push 0    return this     call     5        gt   0  0  0  0  0    A bit shorter with for-loop    function n    for  n-- this push 0    return this     call     5        gt   0  0  0  0  0    Works with any Object  just change what s inside this push      You can even save the function   function fill size  content      for  size-- this push content      return this      Call it using   var helloArray   fill call     5   hello         gt    hello    hello    hello    hello    hello     Adding elements to an already existing array   var helloWorldArray   fill call helloArray  5   world         gt    hello    hello    hello    hello    hello    world    world    world    world    world     Performance  http   jsperf com zero-filled-array-creation 25

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To create an all new Array  new Array arrayLength  fill 0     To add some values at the end of an existing Array      existingArray     new Array numberOfElementsToAdd  fill 0    Example   x000D   x000D      To create an all new Array   x000D   x000D  console log new Array 5  fill 0    x000D   x000D      To add some values at the end of an existing Array   x000D   x000D  let existingArray    1 2 3  x000D   x000D  console log     existingArray     new Array 5  fill 0     x000D   x000D   x000D

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Elegant way to fill an array with precomputed values  Here is another way to do it using ES6 that nobody has mentioned so far    gt  Array from Array 3        gt  0   lt   0  0  0    It works by passing a map function as the second parameter of Array from   In the example above  the first parameter allocates an array of 3 positions filled with the value undefined and then the lambda function maps each one of them to the value 0   Although Array len  fill 0  is shorter  it doesn t work if you need to fill the array by doing some computation first  I know the question didn t ask for it  but a lot of people end up here looking for this    For instance  if you need an array with 10 random numbers    gt  Array from Array 10        gt  Math floor 10   Math random      lt   3  6  8  1  9  3  0  6  7  1    It s more concise  and elegant  than the equivalent   const numbers   Array 10   for  let i   0  i  lt  numbers length  i          numbers i    Math round 10   Math random         This method can also be used to generate sequences of numbers by taking advantage of the index parameter provided in the callback    gt  Array from Array 10    d  i    gt  i   lt   0  1  2  3  4  5  6  7  8  9      Bonus answer  fill an array using String repeat    Since this answer is getting a good deal of attention  I also wanted to show this cool trick  Although not as useful as my main answer  will introduce the still not very known  but very useful String repeat   method  Here s the trick    gt      repeat 10  split     map      gt  Math floor 10   Math random      lt   5  6  3  5  0  8  2  7  4  1    Cool  huh  repeat   is a very useful method to create a string that is the repetition of the original string a certain number of times  After that  split   creates an array for us  which is then map  ped to the values we want  Breaking it down in steps    gt      repeat 10   lt                 gt      repeat 10  split      lt                                                       gt      repeat 10  split     map      gt  Math floor 10   Math random      lt   5  6  3  5  0  8  2  7  4  1

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var str    0000000   0000   var arr   str split        usage in expressions  arr i  1   EDIT  if arr supposed to be used in integer expressions  then please don t mind the char value of  0   You just use it as follows    a   a   arr i   assuming a has integer value

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Didn t see this method in answers  so here it is    0  repeat  200   split     map  parseFloat     In result you will get zero-valued array of length 200     0  0  0  0      0     I m not sure about the performance of this code  but it shouldn t be an issue if you use it for relatively small arrays

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I know this isn t the purpose of the question  but here s an out-of-the-box idea  Why  My CSci professor noted that there is nothing magical about  cleansing  data with zero  So the most efficient way is to NOT do it at all  Only do it if the data needs to be zero as an initial condition  as for certain summations  -- which is usually NOT the case for most applications

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The way I usually do it  and is amazing fast  is using Uint8Array  For example  creating a zero filled vector of 1M elements     var zeroFilled      slice apply new Uint8Array 1000000     I m a Linux user and always have worked for me  but once a friend using a Mac had some non-zero elements  I thought his machine was malfunctioning  but still here s the safest way we found to fix it     var zeroFilled      slice apply new Uint8Array new Array 1000000      Edited  Chrome 25 0 1364 160   Frederik Gottlieb - 6 43 Sam Barnum - 4 83 Eli - 3 68 Joshua 2 91 Mathew Crumley - 2 67 bduran - 2 55 Allen Rice - 2 11 kangax - 0 68 Tj  Crowder - 0 67 zertosh - ERROR   Firefox 20 0   Allen Rice - 1 85 Joshua - 1 82 Mathew Crumley - 1 79 bduran - 1 37 Frederik Gottlieb - 0 67 Sam Barnum - 0 63 Eli - 0 59 kagax - 0 13 Tj  Crowder - 0 13 zertosh - ERROR   Missing the most important test  at least for me   the Node js one  I suspect it close to Chrome benchmark

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ES6 solution       new Array 5   map x   gt  0       0  0  0  0  0

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The fastest here is    arr       length   len  arr fill 0

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I have nothing against   Array apply null  Array 5   map Number prototype valueOf 0   new Array 5 1  join  0   split     map parseFloat     suggested by Zertosh  but in a new ES6 array extensions allow you to do this natively with fill method  Now IE edge  Chrome and FF supports it  but check the compatibility table  new Array 3  fill 0  will give you  0  0  0   You can fill the array with any value like new Array 5  fill  abc    even objects and other arrays    On top of that you can modify previous arrays with fill   arr    1  2  3  4  5  6  arr fill 9  3  5     what to fill  start  end   which gives you   1  2  3  9  9  6

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It might be worth pointing out  that Array prototype fill had been added as part of the ECMAScript 6  Harmony  proposal  I would rather go with the polyfill written below  before considering other options mentioned on the thread   if   Array prototype fill      Array prototype fill   function value            Steps 1-2      if  this    null          throw new TypeError  this is null or not defined               var O   Object this           Steps 3-5      var len   O length  gt  gt  gt  0          Steps 6-7      var start   arguments 1       var relativeStart   start  gt  gt  0          Step 8      var k   relativeStart  lt  0         Math max len   relativeStart  0          Math min relativeStart  len           Steps 9-10      var end   arguments 2       var relativeEnd   end     undefined         len   end  gt  gt  0          Step 11      var final   relativeEnd  lt  0         Math max len   relativeEnd  0          Math min relativeEnd  len           Step 12      while  k  lt  final          O k    value        k                  Step 13      return O

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lodash     fill array  value    is a clean and cross-browser safe way to fill an array

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If you use ES6  you can use Array from   like this   Array from   length  3         gt  0      0  0  0    Has the same result as  Array from   length  3    map      gt  0     0  0  0    Because   Array from   length  3       undefined  undefined  undefined

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Recursive solutions  As noted by several others  utilizing  concat   generally provides fast solutions  Here is a simple recursive solution    x000D   x000D  function zeroFill len  a   x000D    return len  lt    a     a    0    length   x000D      a slice 0  len    x000D      zeroFill len  a concat a   x000D    x000D   x000D  console log zeroFill 5    x000D   x000D   x000D    And a general-purpose recursive array fill function    x000D   x000D  function fill len  v   x000D    return len  lt    v      concat v  v   length   x000D      v slice 0  len    fill len  v  x000D    x000D   x000D  console log fill 5   abc     x000D   x000D   x000D

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function zeroFilledArray size        return new Array size   1  join  0   split

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Note added August 2013  updated February 2015  The answer below from 2009 relates to JavaScript s generic Array type  It doesn t relate to the newer typed arrays defined in ES2015  and available now in many browsers   like Int32Array and such  Also note that ES2015 adds a fill method to both Arrays and typed arrays  which is likely to be the most efficient way to fill them     Also  it can make a big difference to some implementations how you create the array  Chrome s V8 engine  in particular  tries to use a highly-efficient  contiguous-memory array if it thinks it can  shifting to the object-based array only when necessary     With most languages  it would be pre-allocate  then zero-fill  like this   function newFilledArray len  val        var rv   new Array len       while  --len  gt   0            rv len    val            return rv      But  JavaScript arrays aren t really arrays  they re key value maps just like all other JavaScript objects  so there s no  pre-allocate  to do  setting the length doesn t allocate that many slots to fill   nor is there any reason to believe that the benefit of counting down to zero  which is just to make the comparison in the loop fast  isn t outweighed by adding the keys in reverse order when the implementation may well have optimized their handling of the keys related to arrays on the theory you ll generally do them in order   In fact  Matthew Crumley pointed out that counting down is markedly slower on Firefox than counting up  a result I can confirm nbsp  mdash  it s the array part of it  looping down to zero is still faster than looping up to a limit in a var   Apparently adding the elements to the array in reverse order is a slow op on Firefox  In fact  the results vary quite a bit by JavaScript implementation  which isn t all that surprising   Here s a quick and dirty test page  below  for browser implementations  very dirty  doesn t yield during tests  so provides minimal feedback and will run afoul of script time limits   I recommend refreshing between tests  FF  at least  slows down on repeated tests if you don t   The fairly complicated version that uses Array concat is faster than a straight init on FF as of somewhere between 1 000 and 2 000 element arrays   On Chrome s V8 engine  though  straight init wins out every time     Here s the test page  live copy     lt  DOCTYPE html gt   lt html gt   lt head gt   lt meta charset  UTF-8  gt   lt title gt Zero Init Test Page lt  title gt   lt style type  text css  gt  body       font-family     sans-serif     log p       margin      0      padding     0     error       color       red     winner       color       green      font-weight     bold     lt  style gt   lt script type  text javascript  src  prototype-1 6 0 3 js  gt  lt  script gt   lt script type  text javascript  gt  var testdefs          downpre              total   0          desc     Count down  pre-decrement           func    makeWithCountDownPre             downpost             total   0          desc     Count down  post-decrement           func    makeWithCountDownPost             up                   total   0          desc     Count up  normal            func    makeWithCountUp             downandup              total   0          desc     Count down  for loop  and up  for filling            func    makeWithCountDownArrayUp             concat               total   0          desc     Concat           func    makeWithConcat           document observe  dom loaded   function         var markup  defname       markup           for  defname in testdefs            markup                  lt div gt  lt input type  checkbox  id  chk     defname      checked gt                   lt label for  chk     defname      gt     testdefs defname  desc     lt  label gt  lt  div gt                 checkboxes   update markup          btnTest   observe  click   btnTestClick        function epoch         return  new Date    getTime       function btnTestClick             Clear log        log   update  Testing               Show running        btnTest   disabled   true          Run after a pause while the browser updates display     btnTestClickPart2 defer      function btnTestClickPart2          try           runTests              catch  e            log  Exception      e                 Re-enable the button  we don t yheidl        btnTest   disabled   false     function runTests         var start  time  counter  length  defname  def  results  a  invalid  lowest  s          Get loops and length     s    F  txtLoops        runcount   parseInt s       if  isNaN runcount     runcount  lt   0            log  Invalid loops value      s                 return            s    F  txtLength        length   parseInt s       if  isNaN length     length  lt   0            log  Invalid length value      s                 return                Clear log        log   update              Do it     for  counter   0  counter  lt   runcount    counter             for  defname in testdefs                def   testdefs defname               if     chk     defname  checked                    start   epoch                    a   def func length                   time   epoch   - start                  if  counter    0                           Don t count  warm up   but do check the algorithm works                     invalid   validateResult a  length                       if  invalid                            log   lt span class  error  gt FAILURE lt  span gt  with def     defname          invalid                           return                                                          else                          Count this one                     log       counter          def desc          time    ms                        def total    time                                                       for  defname in testdefs            def   testdefs defname           if     chk     defname  checked                def avg   def total   runcount              if  typeof lowest     number     lowest  gt  def avg                    lowest   def avg                                     results             lt p gt Results               lt br gt Length      length             lt br gt Loops      runcount             lt  p gt        for  defname in testdefs            def   testdefs defname           if     chk     defname  checked                results      lt p     lowest    def avg     class  winner             gt     def desc      average time      def avg    ms lt  p gt                        results      lt hr gt           log   insert  top  results       function validateResult a  length        var n       if  a length    length            return  Length is wrong             for  n   length - 1  n  gt   0  --n            if  a n     0                return  Index     n     is not zero                       return undefined     function makeWithCountDownPre len        var a       a   new Array len       while  --len  gt   0            a len    0            return a     function makeWithCountDownPost len        var a       a   new Array len       while  len--  gt  0            a len    0            return a     function makeWithCountUp len        var a  i       a   new Array len       for  i   0  i  lt  len    i            a i    0            return a     function makeWithCountDownArrayUp len        var a  i       a   new Array len       i   0      while  --len  gt   0            a i      0            return a     function makeWithConcat len        var a  rem  currlen       if  len    0            return               a    0       currlen   1      while  currlen  lt  len            rem   len - currlen          if  rem  lt  currlen                a   a concat a slice 0  rem                      else               a   a concat a                     currlen   a length            return a     function log msg           log   appendChild new Element  p   update msg       lt  script gt   lt  head gt   lt body gt  lt div gt   lt label for  txtLength  gt Length  lt  label gt  lt input type  text  id  txtLength  value  10000  gt   lt br gt  lt label for  txtLoops  gt Loops  lt  label gt  lt input type  text  id  txtLoops  value  10  gt   lt div id  checkboxes  gt  lt  div gt   lt br gt  lt input type  button  id  btnTest  value  Test  gt   lt hr gt   lt div id  log  gt  lt  div gt   lt  div gt  lt  body gt   lt  html gt

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What everyone else seems to be missing is setting the length of the array beforehand so that the interpreter isn t constantly changing the size of the array   My simple one-liner would be Array prototype slice apply new Uint8Array length    But if I were to create a function to do it fast without some hacky workaround  I would probably write a function like this   var filledArray   function value  l        var i   0  a       a length   l      while i lt l  a i      value      return a

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If you need to create many zero filled arrays of different lengths during the execution of your code  the fastest way I ve found to achieve this is to create a zero array once  using one of the methods mentioned on this topic  of a length which you know will never be exceeded  and then slice that array as necessary   For example  using the function from the chosen answer above to initialize the array   create a zero filled array of length maxLength  as a variable visible to the code that needs zero arrays   var zero   newFilledArray maxLength  0     Now slice this array everytime you need a zero filled array of length requiredLength  lt  maxLength   zero slice 0  requiredLength     I was creating zero filled arrays thousands of times during execution of my code  this speeded up the process tremendously

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I knew I had this proto d somewhere     Array prototype init   function x n        if typeof n    undefined     n   this length        while  n--    this n    x        return this     var a    new Array 5   init 0    var b      init 0 4     Edit  tests  In response to Joshua and others methods I ran my own benchmarking  and I m seeing completely different results to those reported   Here s what I tested     my original method Array prototype init   function x n        if typeof n    undefined     n   this length        while  n--    this n    x        return this       now using push which I had previously thought to be slower than direct assignment Array prototype init2   function x n        if typeof n    undefined     n   this length        while  n--    this push x         return this       joshua s method function newFilledArray len  val        var a           while len--           a push val             return a       test m1 and m2 with short arrays many times 10K   10  var a   new Date    for var i 0  i lt 10000  i          var t1      init 0 10     var A   new Date     var b   new Date    for var i 0  i lt 10000  i          var t2      init2 0 10     var B   new Date       test m1 and m2 with long array created once 100K  var c   new Date    var t3      init 0 100000   var C   new Date     var d   new Date    var t4      init2 0 100000   var D   new Date       test m3 with short array many times 10K   10  var e   new Date    for var i 0  i lt 10000  i          var t5   newFilledArray 10 0     var E   new Date       test m3 with long array created once 100K  var f   new Date    var t6   newFilledArray 100000  0  var F   new Date      Results   IE7 deltas  dA 156 dB 359 dC 125 dD 375 dE 468 dF 412  FF3 5 deltas  dA 6 dB 13 dC 63 dD 8 dE 12 dF 8   So by my reckoning push is indeed slower generally but performs better with longer arrays in FF but worse in IE which just sucks in general  quel surprise

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return Array  quantity   fill 1  map  n   gt  return n   Math abs    Math random      1000 - 1   1     1      One line

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Shortest for loop code  a i    for  i lt 100  a i    0   edit  for a i    i lt 100  a i    0  or for a    i 100 i--  a i  0    Safe var version  var a    i 0 for  i lt 100  a i    0   edit  for var i 100 a    i--  a i  0

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My fastest function would be   function newFilledArray len  val        var a           while len--           a push val             return a     var st    new Date    getTime    newFilledArray 1000000  0  console log  new Date    getTime   - st      returned 63  65  62 milliseconds   Using the native push and shift to add items to the array is much faster  about 10 times  than declaring the array scope and referencing each item to set it s value   fyi  I consistently get faster times with the first loop  which is counting down  when running this in firebug  firefox extension    var a       var len   1000000  var st    new Date    getTime    while len       a push 0       len -  1    console log  new Date    getTime   - st      returned 863  894  875 milliseconds st    new Date    getTime    len   1000000  a       for var i   0  i  lt  len  i         a push 0     console log  new Date    getTime   - st      returned 1155  1179  1163 milliseconds   I m interested to know what T J  Crowder makes of that    -

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I ve tested all combinations of pre-allocating not pre-allocating  counting up down  and for while loops in IE 6 7 8  Firefox 3 5  Chrome  and Opera   The functions below was consistently the fastest or extremely close in Firefox  Chrome  and IE8  and not much slower than the fastest in Opera and IE 6  It s also the simplest and clearest in my opinion  I ve found several browsers where the while loop version is slightly faster  so I m including it too for reference   function newFilledArray length  val        var array           for  var i   0  i  lt  length  i              array i    val            return array      or  function newFilledArray length  val        var array           var i   0      while  i  lt  length            array i      val            return array

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The fastest way to do that is with forEach      we keep backward compatibility for IE  lt  9   var fillArray   Array prototype forEach       function arr  n             arr forEach function    index    arr index    n               return arr                function arr  n             var len   arr length           arr length   0           while len--  arr push n            return arr               test fillArray  1 2 3    X         gt    X    X    X

User · Answer

Using lodash or underscore    range 0  length - 1  0     Or if you have an array existing and you want an array of the same length  array map   constant 0

[javascript] Most efficient way to create a zero filled JavaScript array?

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