Determine calling function in javascript

Question

How can I find out in a javascript function which was the calling (the former in the call stack) function?

I would like to determine if the former called function is a __doPostback in the onbeforeunload event.

Answer 1

Each function has a caller property defined.

From https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Global_Objects/Function/caller:

function myFunc() {
    if (myFunc.caller == null) {
        return ("The function was called from the top!");
    } else
        return ("This function's caller was " + myFunc.caller);
    }
}

The Function.caller property is not part of the ECMA3 standard but it's implemented across all major browsers, including IE and Firefox.

If you're using an anonymous function, you can still access the caller property via the arguments.calee property:

function() {
    if (arguments.callee.caller == null) {
        return ("The function was called from the top!");
    } else
        return ("This function's caller was " + arguments.callee.caller);
    }
}

Note that this code is accessing the current function, and then referencing the same non-standard caller property on it. This is distinct from using the deprecated arguments.caller property directly, which is not implemented in some modern browsers.