Create an array with same element repeated multiple times

Question

In Python  where  2  is a list  the following code gives this output    2    5   Outputs   2 2 2 2 2    Does there exist an easy way to do this with an array in JavaScript   I wrote the following function to do it  but is there something shorter or better   var repeatelem   function elem  n          returns an array with element elem repeated n times      var arr            for  var i   0  i  lt   n  i              arr   arr concat elem               return arr

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You can use the SpreadOpeator and the map   function to create an array with the same element repeated multiple times  function fillArray value len          return     Array len  keys    map x  gt  value

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x000D   x000D  var finalAry        2  repeat 5  split      map Number   x000D  console log finalAry   x000D   x000D   x000D

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If you need to repeat an array  use the following  Array 3  fill   a   b   c    flat     will return Array 9     quot a quot    quot b quot    quot c quot    quot a quot    quot b quot    quot c quot    quot a quot    quot b quot    quot c quot

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No easier way  You need to make a loop and push elements into the array

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I had problems with the mentioned methods when I use an array like  var array     foo    bar    foobar    var filled   array fill 7      filled should be   foo    bar    foobar    foo    bar    foobar    foo     To get this I m using   Array prototype fill   function val       var l   this length      if l  lt  val           for var i   val-1-l  i  gt   0  i--               this i l    this i   l                       return this

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In ES6 using Array fill   method  Array 5  fill 2      gt   2  2  2  2  2

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Try This    avinash   repeat 5  trim   split

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I needed a way to repeat loop an array  with n items  m times   For example  distributing a list  of persons  to a week month  Let s say I have 3 names  and I want to them to repeat in a week   fillArray   Adam    Blair    Curtis    7      returns   Adam    Blair    Curtis    Adam    Blair    Curtis    Adam       function fillArray pattern  count        let result           if    number    string   includes typeof pattern             result   new Array 5           result fill pattern             else if  pattern instanceof Array            for  let i   0  i  lt  count  i                  result   result concat pattern                     result   result slice 0  count             return result     fillArray  a   5               a    a    a    a    a   fillArray 1  5                1  1  1  1  1  fillArray   a    b    5        a    b    a    b    a

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Can be used as a one-liner too   function repeat arr  len        while  arr length  lt  len  arr   arr concat arr slice 0  len-arr length        return arr

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In case you need to repeat an array several times   var arrayA     a   b   c    var repeats   3  var arrayB   Array apply null   length  repeats   arrayA length            map function e i  return arrayA i   arrayA length        result  arrayB     a   b   c   a   b   c   a   b   c     inspired by this answer

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you can try   Array 6  join  a   split         returns   a   a   a   a   a    5 times    Update  01 06 2018    Now you can have a set of characters repeating   new Array 5  fill  a       give the same result as above     or Array from   length  5    fill  a     Note  Check more about fill      and from      for compatibility and browser support   Update  05 11 2019    Another way  without using fill or from  that works for string of any length   Array apply null  Array 3   map     gt   abc        abc    abc    abc        Same as above answer  Adding for sake of completeness

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You can also extend the functionality of Array like so   Array prototype fill   function val       for  var i   0  i  lt  this length  i             this i    val            return this        used like  var arry   new Array 5   fill 2      or var arry   new Array 5   arry fill 2      console log arry       2  2  2  2  2     I should note that extending the functionality of built-in objects can cause problems if you are working with 3rd-party libraries  Always weigh this into your decisions

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You can do it like this   function fillArray value  len      if  len    0  return       var a    value     while  a length   2  lt   len  a   a concat a     if  a length  lt  len  a   a concat a slice 0  len - a length      return a      It doubles the array in each iteration  so it can create a really large array with few iterations     Note  You can also improve your function a lot by using push instead of concat  as concat will create a new array each iteration  Like this  shown just as an example of how you can work with arrays    function fillArray value  len      var arr         for  var i   0  i  lt  len  i          arr push value         return arr

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This could be another answers  let cards     quot A 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 J quot   quot Q quot   quot K quot    let totalCards       cards     cards     cards     cards

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In the Node js REPL    gt  Array from  length 5   map x   gt  2    2  2  2  2  2

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gt  gt  gt  Array apply null  Array 10   map function   return 5    5  5  5  5  5  5  5  5  5  5   gt  gt  gt    Or in ES6  gt  gt  gt      Array 10   map     i    gt  5   5  5  5  5  5  5  5  5  5  5

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Use this function   function repeatElement element  count        return Array count  fill element       gt  gt  gt  repeatElement      5  join               Or for a more compact version   const repeatElement    element  count    gt      Array count  fill element     gt  gt  gt  repeatElement      5  join               Or for a curry-able version   const repeatElement   element   gt  count   gt      Array count  fill element     gt  gt  gt  repeatElement      5  join               You can use this function with a list   const repeatElement    element  count    gt      Array count  fill element    gt  gt  gt    a    b      repeatElement  c   5     a    b    c    c    c    c    c

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Improving on Vivek s answer  this works for strings of any length  to populate an array of length n  Array n 1  join   string to be repeated  separator    split   separator    slice 0  n

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c    n can be written as   Array n 1  join 1  split     map function   return c      so for  2    5  Array 6  join 1  split     map function   return 2

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and Array fill   comes to the rescue   Used to write it all manually before knowing this one        x000D   x000D  Array length  fill value     Array 5  fill         gt                     Array 3  fill   value  2        gt      value  2     value  2     value  2    x000D   x000D   x000D

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Another one-liner   Array prototype map call    Array 5 1  function    return  2

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If you are using a utlity belt like lodash underscore you can do it like this     let result     map   times foo   function    return bar

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Array from  length 5   i   gt  1      1  1  1  1  1   or create array with increasing value   Array from  length 5    e  i   gt i      0  1  2  3  4

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I discovered this today while trying to make a 2D array without using loops  In retrospect  joining a new array is neat  I tried mapping a new array  which doesn t work as map skips empty slots       repeat 5  split     map x   gt  0    The     char can be any valid single character  The 5 would be a variable for the number of elements you want  The 7 would be the value you want to fill your array with   The new fill method is better  and when I coded this I didn t know it existed  nor did I know repeat is es6  I m going to write a blog post about using this trick in tandem with reduce to do cool things   http   jburger us to 2016 07 14 functionally-create-a-2d-array

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This function creates an array of  length  elements where each element equals  value  as long as  value  is an integer or string of an integer  Any decimal numbers will be truncated  If you do want decimal numbers  replace  parseInt   with  parseFloat    function fillArray length  intValue         var vals    new Array length   1   join intValue        split      slice 0 length        for var i   0  i  lt  length  i    1             vals i    parseInt vals i                return vals      Examples   fillArray 5  7     returns  7 7 7 7 7  fillArray 5  7 5     returns  7 7 7 7 7  fillArray 5  200     returns  200 200 200 200 200

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In lodash it s not so bad     flatten   times 5  function      return  2            2  2  2  2  2    EDIT  Even better     times 5    constant 2        2  2  2  2  2    EDIT  Even better     fill Array 5   2

[javascript] Create an array with same element repeated multiple times

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