internet-explorer document.title w3schools - What are the common mistakes to avoid when coding javascript for Internet Explorer?

6 Answers

Here's a subtle one: if your site has multiple frames (or iframes), and you've got Javascript code communicating between frames sometimes, IE (6 and 7, not so sure about 8 and 9) is very picky about the "lineage" of Javascript objects, even ones without any DOM references. What that means is that if you communicate a Javascript object of almost any type (strings and numbers are usually OK, but even Date instances have caused me problems in the past) from one frame to another, if at some point later the source frame is updated with a new page, the destination page will get an exception if it tries to mess with that communicated object. Firefox was pretty mellow about that sort of thing, but when IE garbage collects the old page, it thereafter does not like references to the Javascript objects that page created.

get attribute set

I'm about to start coding a new, javascript-heavy website, but before I start I'd like to minimize my debugging time in Internet Explorer by knowing beforehand what the quirks are. I'm not planning to worry too much about IE6.

What are the common mistakes/differences to avoid in javascript code that work fine in other browsers, but break in Internet Explorer?

Concatenate strings with +

var str="";
for (var i = 0; i < max; ++i) {
  str += somefunction(i);

On MSIE it can take several minutes. I once did a test where Opera an Firefox where finished after a few seconds, but MSIE hadn't finished after 20 MINUTES!

However, if using an array, MSIE was fast:

var str = [];
for (var i = 0; i < max; ++i) {
   str.push( somefunction(i));
str = str.join("");

Sorry, but can't find the post I made about it right now.

Be aware of how Internet Explorer handles dom tree parsing and navigation, one in particular, that also exists when parsing httpObjects in general :

  • xmlNode.textContent does not return anything in internet explorer
  • xmlNode.firstChild.nodeValue or something that returns the node value must be used


IE does not support custom events, only DOM events (yes even in 9 beta).

Watch out for little differences like the way iframe borders are handled (How to Remove an IFrame border in Javascript).

I guess the internet-explorer tag should give you lots of good examples.

IE 7/8 fails to understand console.log/dir unless console window opened. This can easily break your JS if you leave any in the prod environment. Always have

   console.log('Hello World')