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javascriptdebuggingfirebug

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

Firebug console scope. Why isn't "this" always the same? Shoudn't it be "window" all the time?

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.