functional way to iterate over range ES6 7

Question

What is the best way to do the below in more functional way  with ES6 ES7   let cols       for  let i  0  i  lt   7  i         cols push i   i     return cols    I tried like   return      7   map i   gt      return i   i        but that translated to      concat 7  map function  n      return n   n        which is not what I expected   EDIT    pavlo  Indeed  that was a mistake  I was using JSX  and for example  I want 7 divs   untested   let cols           for  let i  0  i  lt   7  i             cols push  lt div id  i  gt        lt  div gt             return cols    so the idea was indeed to reduce the number of temp variables and procedural feel

User · Accepted Answer

One can create an empty array  fill it  otherwise map will skip it  and then map indexes to values   Array 8  fill   map     i    gt  i   i

User · Answer

Here s an approach using generators   function  square n        for  var i   0  i  lt  n  i     yield i i      Then you can write  console log    square 7      Another idea is       Array 5   map     i    gt  i i    Array 5  creates an unfilled five-element array  That s how Array works when given a single argument  We use the spread operator to create an array with five undefined elements  That we can then map  See http   ariya ofilabs com 2013 07 sequences-using-javascript-array html   Alternatively  we could write  Array from Array 5   map     i    gt  i i    or  we could take advantage of the second argument to Array from to skip the map and write   Array from Array 5       i    gt  i i    A horrible hack which I saw recently  which I do not recommend you use  is      1e4     map     i    gt  i i

User · Answer

ES7 Proposal  Warning  Unfortunately I believe most popular platforms have dropped support for comprehensions  See below for the well-supported ES6 method  You can always use something like    for  i of Array 7  keys    i i     Running this code on Firefox        0  1  4  9  16  25  36     This works on Firefox  it was a proposed ES7 feature   but it has been dropped from the spec  IIRC  Babel 5 with  experimental  enabled supports this   This is your best bet as array-comprehension are used for just this purpose  You can even write a range function to go along with this   var range    u  l   0    gt    for  i of Array u - l  keys     i   l     Then you can do    for  i of range 5   i i     0  1  4  9  16  25  for  i of range 5 3   i i     9  16  25   ES6  A nice way to do this any of       Array 7  keys    map i   gt  i   i   Array 7  fill   map    i    gt  i i       Array 7   map    i    gt  i i     This will output        0  1  4  9  16  25  36

[javascript] functional way to iterate over range (ES6/7)

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