Firebug console window scope. Why isn't "this" always the same?

debugging, firebug, javascript

Solution

The value of `this` in the console will be the same as the value of `this` in the code currently being executed. Consider:-

function outer()
{
        // this is window

    var x = {n:12};

    var fn = function()
    {
               // this is object {n:12}

        alert(this.n);
    }

    fn.call(x);
}

...

<img src="thing.gif" onclick="outer()" />

If you put a break point on the `x = {n:12}` line, switch to console you will find the `this` is the window. However when you step to the `alert` line `this` in the console is the object held by the `x` variable. IOW there is no distinction between `this` in the executing context and the console. Its for this reason that you can use the console to tweak values of variables and properties while debugging.

Problem

Original source