Javascript for loop error

Question

This is what I have:

function get_bad_changelist_authors() {
   var changelistAuthorDivs = $('div.bad_changelist_author');
   var changelistAuthors = [];

   for (var div in changelistAuthorDivs) {
      changelistAuthors.push($(changelistAuthorDivs[div]).text());
   }

   return changelistAuthors;
}

changeListAuthorDivs has n elements but for some reason it iterates n+1 times and initialized div to a string (ie. the string "length") on the last iteration. On the last iteration is where this loop has its error.

Already tried using a for loop with an explicit indexer? Like for(var i=0;i<list.length;i++) — Bas Slagter
– Bas Slagter, Commented Aug 16, 2011 at 7:57
lol, i was just seriously confused about how div ="length...i find that a strange concept — Nadir Muzaffar
– Nadir Muzaffar, Commented Aug 16, 2011 at 8:07

Felix Kling · Accepted Answer · 2011-08-16 07:53:06Z

2

It seems you are using jQuery (please confirm). Then you can use .map() ^[docs] to achieve the same in a more concise way:

function get_bad_changelist_authors() {
   return $('div.bad_changelist_author').map(function() {
        return $(this).text();
   }).get();
}

Alternatively , use .each() ^[docs] if you deal with jQuery objects.

In general, @James is completely right, don't use for...in to iterate over arrays (see the warning here). In this case, the jQuery object has to be treated like an array.

answered Aug 16, 2011 at 7:53

Felix Kling

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2 Comments

Nadir Muzaffar Over a year ago

Sweet, I think I'll try the map function out. And thanks for pointing out a resource where I can checkup Javascript documentation.

Felix Kling Over a year ago

@Nadir: You are welcome. The jQuery documentation and the Mozilla JavaScript reference and guide are really great. I suggest to read the guide, it will give you some more insight into JavaScript. Happy coding! :)

James Allardice · Accepted Answer · 2011-08-16 07:51:13Z

1

JavaScript for...in loops will also iterate over properties of the object (length is a property of the object, which is why you end up with a div containing that string), which is not what you want. Use a normal for loop instead:

for(var i = 0; i < changeListAuthorDivs.length; i++) {
   //Do stuff
}

answered Aug 16, 2011 at 7:51

James Allardice

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Comments

Eliu · Accepted Answer · 2011-08-16 08:11:08Z

0

Try this

 for (var div in changelistAuthorDivs) {
     if(Object.prototype.hasOwnProperty.call(changelistAuthorDivs[div], div))
     changelistAuthors.push($(changelistAuthorDivs[div]).text());
  }

edited Aug 16, 2011 at 8:11

answered Aug 16, 2011 at 8:01

Eliu

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