how to stop Javascript forEach

Question

I m playing with Node js and Mongoose     trying to find specific comment in deep comments nesting with recursive function and forEach within  Is there a way to stop Node js forEach  As I understand every forEach iteration is a function and and I can t just do break  only return but this won t stop forEach  function recurs comment        comment comments forEach function elem             recurs elem              if      break

User · Answer

You can break from a forEach loop if you overwrite the Array method:

(function(){
    window.broken = false;

        Array.prototype.forEach = function(cb, thisArg) {
            var newCb = new Function("with({_break: function(){window.broken = true;}}){("+cb.replace(/break/g, "_break()")+"(arguments[0], arguments[1], arguments[2]));}");
            this.some(function(item, index, array){
                 newCb(item, index, array);
                 return window.broken;
            }, thisArg);
            window.broken = false;
        }

}())

example:

[1,2,3].forEach("function(x){\
    if (x == 2) break;\
    console.log(x)\
}")

Unfortunately with this solution you can't use normal break inside your callbacks, you must wrap invalid code in strings and native functions don't work directly (but you can work around that)

Happy breaking!

User · Answer

You can use Lodash s forEach function if you don t mind using 3rd party libraries   Example   var     require  lodash       forEach comments  function  comment        do something with comment        if                 return false         Exits the loop

User · Answer

In some cases Array some will probably fulfil the requirements

User · Answer

You can t break from a forEach  I can think of three ways to fake it  though   1  The Ugly Way  pass a second argument to forEach to use as context  and store a boolean in there  then use an if  This looks awful   2  The Controversial Way  surround the whole thing in a try-catch block and throw an exception when you want to break  This looks pretty bad and may affect performance  but can be encapsulated   3  The Fun Way  use  every       a    b    c   every function element  index         Do your thing  then    if  you want to break  return false   else return true      You can use some   instead  if you d rather return true to break

User · Answer

Below code will break the foreach loop once the condition is met  below is the sample example      var array    1 2 3 4 5       var newArray   array slice 0 array length       array forEach function item index             your breaking condition goes here example checking for value 2         if item    2               array length   array indexOf item                         array   newArray

User · Answer

I guess you want to use Array prototype find Find will break itself when it finds your specific value in the array   var inventory        name   apples   quantity  2      name   bananas   quantity  0      name   cherries   quantity  5      function findCherries fruit       return fruit name      cherries      console log inventory find findCherries          name   cherries   quantity  5

User · Answer

forEach does not break on return  there are ugly solutions to get this work but I suggest not to use it  instead try to use Array prototype some or Array prototype every   x000D   x000D  var ar    1 2 3 4 5   x000D   x000D  ar some function item index   x000D    if item    3   x000D       return true  x000D      x000D    console log  item is    item   index is     index   x000D      x000D   x000D   x000D

User · Answer

Array forEach cannot be broken and using try   catch or hacky methods such as Array every or Array some will only make your code harder to understand  There are only two solutions of this problem   1  use a old for loop  this will be the most compatible solution but can be very hard to read when used often in large blocks of code   var testArray     a    b    c    for  var key   0  key  lt  testArray length  key          var value   testArray key       console log key      This is the key      console log value      This is the value      2  use the new ECMA6  2015 specification  in cases where compatibility is not a problem  Note that even in 2016  only a few browsers and IDEs offer good support for this new specification  While this works for iterable objects  e g  Arrays   if you want to use this on non-iterable objects  you will need to use the Object entries method  This method is scarcely available as of June 18th 2016 and even Chrome requires a special flag to enable it  chrome   flags  enable-javascript-harmony  For Arrays  you won t need all this but compatibility remains a problem   var testArray     a    b    c    for  let  key  value  of testArray entries          console log key      This is the key      console log value      This is the value      3  A lot of people would agree that neither the first or second option are good candidates  Until option 2 becomes the new standard  most popular libraries such as AngularJS and jQuery offer their own loop methods which can be superior to anything available in JavaScript  Also for those who are not already using these big libraries and that are looking for lightweight options  solutions like this can be used and will almost be on par with ECMA6 while keeping compatibility with older browsers

User · Answer

Breaking out of Array forEach is not possible   You can inspect the source code that implements it in Firefox on the linked page  to confirm this    Instead you should use a normal for loop   function recurs comment        for  var i   0  i  lt  comment comments length    i            var subComment   comment comments i           recurs subComment           if                     break                       or  if you want to be a little more clever about it and comment comments i  is always an object    function recurs comment        for  var i   0  subComment  subComment   comment comments i     i            recurs subComment           if                     break

User · Answer

var f    how to stop Javascript forEach   split           f forEach function  a b           console info b 1           if  a     stop                 console warn   tposition    stop      b 1      r n tall length       f length                 f length   0     lt --

User · Answer

As others have pointed out  you can t cancel a forEach loop  but here s my solution   ary forEach function loop        if loop stop   return         if condition   loop stop   true          Of course this doesn t actually break the loop  it just prevents code execution on all the elements following the  break

User · Answer

Wy not use plain return    function recurs comment   comment comments forEach function elem       recurs elem       if      return        it will return from  recurs  function  I use it like this  Althougth this will not break from  forEach but from whole function  in this simple example it might work

User · Answer

jQuery provides an each   method  not forEach     You can break out of each by returning false   forEach   is part of the ECMA-262 standard  and the only way to break out of that that I m aware of is by throwing an exception   function recurs comment      try       comment comments forEach function elem          recurs elem         if       throw  done               catch  e    if  e     done   throw e        Ugly  but does the job

[javascript] how to stop Javascript forEach?

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