Incorrect handling of the this-keyword in the global scope by IE7

If you define a function as a member of the window object in IE7, the keyword this obviously refers to the wrong object:

window.myFunction = function() {
   return (this === window);

A call to myfunction() in IE7 would incorrecty yield false. This problem also affects exception handling. Predefined event-handlers like onload are not affected.

Test page Workaround is included
Reported by: Arnold Konrad.

Explorer 5-6 Windows, Explorer 7 | Reported on 20 March 2007.

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1 Posted by Eric Gerds on 23 March 2007 | Permalink

The 'this' keyword does indeed point to the window object. The problem is that (this==window) gives the wrong result, whereas (window==this) gives the correct result. Definitely a bug, though.

function Z(){
window.a = function(){

alert((this==window) + "\n" + (window==this) + "\n" + this.Z)



2 Posted by Arnold Konrad on 24 March 2007 | Permalink

The really annoying thing about this bug is that it affects exception handling:

function Z(){
window.a = function(){

throw new Error("Something went wrong!");


try {
} catch(e) {

The above example won't work in IE.

3 Posted by Eric Gerds on 25 March 2007 | Permalink

Yep, definitely a bug.

Add: "var a = null" in front of your code, then it works for me.

Don't know why though.