For In loops in JavaScript - key value pairs

Question

I was wondering if there s a way to do something like a PHP foreach loop in JavaScript  The functionality I m looking for is something like this PHP Snippet   foreach  data as  key   gt   value        I was looking at the JS for  in loop  but there seems to be no way to specify the as  If I do this with a  normal  for loop  for var i   0  i  lt  data length  i     is there a way to grab the key    value pairs

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Below is an example that gets as close as you get   for var key in data     var value   data key           your processing here     If you re using jQuery see  http   api jquery com jQuery each

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for  var k in target       if  target hasOwnProperty k              alert  Key is     k      value is     target k              hasOwnProperty is used to check if your target really has that property  rather than having inherited it from its prototype  A bit simpler would be   for  var k in target       if  typeof target k       function              alert  Key is     k      value is    target k              It just checks that k is not a method  as if target is array you ll get a lot of methods alerted  e g  indexOf  push  pop etc

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If you are using Lodash  you can use   forEach    forEach    a   1   b   2    function value  key      console log key          value            gt  Logs  a  1  then  b  2   iteration order is not guaranteed

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I assume you know that i is the key and that you can get the value via data i   and just want a shortcut for this    ECMAScript5 introduced forEach  MDN  for arrays  it seems you have an array    data forEach function value  index           The MDN documentation provides a shim for browsers not supporting it   Of course this does not work for objects  but you can create a similar function for them   function forEach object  callback        for var prop in object            if object hasOwnProperty prop                 callback prop  object prop                        Since you tagged the question with jquery  jQuery provides   each  docs  which loops over both  array and object structures

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There are three options to deal with keys and values of an object   Select values   Object values obj  forEach value   gt          Select keys   Object keys obj  forEach key   gt          Select keys and values   Object entries obj  forEach   key  value    gt

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for  var key in myMap        if  myMap hasOwnProperty key             console log  key      key           console log  value      myMap key              In javascript  every object has a bunch of built-in key-value pairs that have meta-information  When you loop through all the key-value pairs for an object you re looping through them too  The use of hasOwnProperty   filters these out

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ES6 will provide Map prototype forEach callback  which can be used like this  myMap forEach function value  key  myMap                               Do something

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In the last few year since this question was made  Javascript has added a few new features    One of them is the Object Entries method   Copied directly from MDN is the follow code snippet   const object1       a   somestring     b  42     for  let  key  value  of Object entries object1       console log    key     value

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Please try the below code   lt script gt    const games        quot Fifa quot    quot 232 quot      quot Minecraft quot    quot 476 quot      quot Call of Duty quot    quot 182 quot       Object keys games  forEach  item  index  array    gt      var msg   item     games item     console log msg

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why not simply this var donuts       type   quot Jelly quot   cost  1 22      type   quot Chocolate quot   cost  2 45      type   quot Cider quot   cost  1 59      type   quot Boston Cream quot   cost  5 99      donuts forEach v   gt   console log v  quot type quot     quot  donuts cost   quot  v  quot cost quot    quot  each quot

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for   in will work for you    for  var key in obj       var value   obj key       In modern JavaScript you can also do this   for   const  key value  of Object entries  obj

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yes  you can have associative arrays also in javascript   var obj          name  some name       otherProperty  prop value       date  new Date      for i in obj        var propVal   obj i      i is the key  and obj i  is the value

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No one has mentioned Object keys so I ll mention it   Object keys obj  forEach function  key          do something with obj key

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If you can use ES6 natively or with Babel  js compiler  then you could do the following    x000D   x000D  const test    a  1  b  2  c  3   x000D   x000D  for  const  key  value  of Object entries test     x000D    console log key  value   x000D    x000D   x000D   x000D    Which will print out this output   a 1 b 2 c 3   The Object entries   method returns an array of a given object s own enumerable property  key  value  pairs  in the same order as that provided by a for   in loop  the difference being that a for-in loop enumerates properties in the prototype chain as well     Object entries documentation for   of documentation Destructuring assignment documentation Enumerability and ownership of properties documentation   Hope it helps

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You can use a  for in  loop for this   for  var key in bar         var value   bar key

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You can use the for  in for that   for  var key in data        var value   data key

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let test    a  1  b  2  c  3   Object entries test  forEach   key  value     gt  console log key  value       a 1    b 2    c 3

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var obj          for  var key in obj        var value   obj key        The php syntax is just sugar

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var global    function        return this            Pair object  similar to Python  function Pair key  value        this key   key      this value   value       this toString   function            return       key          value                         as function     param  String  dataName A String holding the name of your pairs list      return  Array Pair  The data list filled       with all pair objects      Object prototype as   function dataName        var value  key  data      global dataName    data            for  key in this           if  this hasOwnProperty key               value   this key               function                  var k   key                   v   value               data push new Pair k  v                                        return data      var d         one   1      two   2        Loop on your  key  list  pairs in this way for  var i   0  max   d as  data   length  i  lt  max  i    1       key   data i  key     value   data i  value      console log  key      key      value      value         delete data when u ve finished with it  delete data

[javascript] For..In loops in JavaScript - key value pairs

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