Javascript Set all values of an array

Question

Code  var cool   new Array 3   cool setAll    42    cool setAll  is just a pseudo selector   alert cool     Result  A alert message   42 42 42   How do I change set all values of an array to a specific value

User · Answer

The ES6 approach is very clean  So first you initialize an array of x length  and then call the fill method on it   let arr   new Array 3  fill 9    this will create an array with 3 elements like    9  9  9

User · Answer

Use a for loop and set each one in turn

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There s no built-in way  you ll have to loop over all of them   function setAll a  v        var i  n   a length      for  i   0  i  lt  n    i            a i    v            http   jsfiddle net alnitak xG88A   If you really want  do this   Array prototype setAll   function v        var i  n   this length      for  i   0  i  lt  n    i            this i    v             and then you could actually do cool setAll 42   see http   jsfiddle net alnitak ee3hb     Some people frown upon extending the prototype of built-in types  though   EDIT ES5 introduced a way to safely extend both Object prototype and Array prototype without breaking for     in     enumeration   Object defineProperty Array prototype   setAll         value  function v                            EDIT 2 In ES6 draft there s also now Array prototype fill  usage cool fill 42

User · Answer

map is the most logical solution for this problem   let xs    1  2  3   xs   xs map x   gt  42   xs    - gt   42  42  42    However  if there is a chance that the array is sparse  you ll need to use for or  even better  for    of   See    https   developer mozilla org en-US docs JavaScript Reference Global Objects Array map https   developer mozilla org en-US docs Web JavaScript Reference Statements for   of

User · Answer

Actually  you can use this perfect approach   let arr   Array apply null  Array 5   map      gt  0       0  0  0  0  0    This code will create array and fill it with zeroes  Or just   let arr   new Array 5  fill 0

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The other answers are Ok  but a while loop seems more appropriate   function setAll array  value      var i   array length    while  i--        array i    value          A more creative version   function replaceAll array  value      var re   new RegExp value   g      return new Array   array length  toString   replace    g  value  match re       May not work everywhere though   -

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It s 2019 and you should be using this   let arr       Array 20   fill 10   So basically 20 is the length or a new instantiated Array

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Found this while working with Epicycles - clearly works - where  p  is invisible to my eyes      Convert a set of picture points to a set of Cartesian coordinates    function toCartesian points  scale      const x max   Math max    points map p  gt p 0       y max   Math max    points map p  gt p 1       x min   Math min    points map p  gt p 0       y min   Math min    points map p  gt p 1       signed x max   Math floor  x max - x min   1    2     signed y max   Math floor  y max - y min   1    2      return points map p  gt      -scale    signed x max - p 0    x min     scale    signed y max - p 1    y min

[javascript] Javascript | Set all values of an array

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