In nodeJs is there a way to loop through an array without using array size

Question

Let s say I have   myArray     item1    item2     I tried   for  var item in myArray   console log item     It prints     0     1  What I wish is to have      item1     item2  Is there any other syntax that works without using   for  var i   0  i  lt  myArray length  i

User · Answer

var count 0      let myArray      1   a   2   b   3   c   4   d        var data   JSON parse myArray       for  let key in data          let value    data key      get the value by key       console log  key    value    key  value         count   count   1           console log  size   count

User · Answer

You can use Array forEach   x000D   x000D  var myArray     1   2  3 4  x000D   x000D  myArray forEach function value   x000D    console log value   x000D      x000D   x000D   x000D

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In ES5 there is no efficient way to iterate over a sparse array without using the length property  In ES6 you can use for   of  Take this examples    x000D   x000D   use strict   x000D   x000D  var arr     one    two   undefined  3  4   x000D      output  x000D   x000D  arr 6     five   x000D   x000D  output       x000D  arr forEach function  val    x000D      output    val        x000D      x000D  console log output   x000D   x000D  output       x000D  for  var i   0  i  lt  arr length  i      x000D      output    arr i         x000D    x000D  console log output   x000D   x000D  output       x000D  for  var val of arr    x000D      output    val        x000D     x000D  console log output   x000D   lt  -- results pane console output  see http   meta stackexchange com a 242491 -- gt  x000D   lt script src    gh-canon github io stack-snippet-console console min js  gt  lt  script gt  x000D   x000D   x000D    All array methods which you can use to iterate safely over dense arrays use the length property of an object created by calling ToObject internaly  See for instance the algorithm used in the forEach method  http   www ecma-international org ecma-262 5 1  sec-15 4 4 18 However in es6  you can use for   of safely for iterating over sparse arrays   See also Are Javascript arrays sparse

User · Answer

What you probably want is for   of  a relatively new construct built for the express purpose of enumerating the values of iterable objects    x000D   x000D  let myArray     a   b   c   d    x000D  for  let item of myArray    x000D    console log item   x000D    x000D   x000D   x000D        as distinct from for   in  which enumerates property names  presumably1 numeric indices in the case of arrays   Your loop displayed unexpected results because you didn t use the property names to get  the corresponding values via bracket notation    but you could have    x000D   x000D  let myArray     a   b   c   d    x000D  for  let key in myArray    x000D    let value    myArray key      get the value by key x000D    console log  key   o  value   o   key  value   x000D    x000D   x000D   x000D    1 Unfortunately  someone may have added enumerable properties to the array or its prototype chain which are not numeric indices    or they may have assigned an index leaving unassigned indices in the interim range  The issues are explained pretty well here  The main takeaway is that it s best to loop explicitly from 0 to array length - 1 rather than using for   in   So  this is not  as I d originally thought  an academic question  i e       Without regard for practicality  is it possible to avoid length when iterating over an array    According to your comment  emphasis mine             why do I need to calculate the size of an array whereas the interpreter can know it    You have a misguided aversion to Array length  It s not calculated on the fly  it s updated whenever the length of the array changes  You re not going to see performance gains by avoiding it  apart from caching the array length rather than accessing the property      Now  even if you did get some marginal performance increase  I doubt it would be enough to justify the risk of dealing with the aforementioned issues

User · Answer

Use the built-in Javascript function called map    map   will do the exact thing you re looking for

User · Answer

This is the natural javascript option   x000D   x000D  var myArray     1   2  3 4  x000D   x000D  myArray forEach function value   x000D    console log value   x000D      x000D   x000D   x000D    However it won t work if you re using await inside the forEach loop because forEach is not asynchronous  you ll be forced to use the second answer or some other equivalent     x000D   x000D  let myArray     a   b   c   d    x000D  for  let item of myArray    x000D    console log item   x000D    x000D   x000D   x000D    Or you could create an asyncForEach explained here      https   codeburst io javascript-async-await-with-foreach-b6ba62bbf404

User · Answer

Use Iterators     var myarray     hello     hello again    processArray myarray Symbol iterator          gt        console log  all done      function processArray iter  cb        var curr   iter next       if curr done          return cb       console log curr value      processArray iter  cb      More in depth overview  https   developer mozilla org en-US docs Web JavaScript Reference Iteration protocols

User · Answer

To print  item1     item2   this code would work   var myarray     hello     hello again     for  var item in myarray        console log myarray item

[javascript] In nodeJs is there a way to loop through an array without using array size?

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