Question

If I have an arbitrary function myFunc, what I’m aiming to do is replace this function with a wrapped call that runs code before and after it executes, e.g.

// note: psuedo-javascript

var beforeExecute = function() { ... }
var afterExecute = function() { ... }

myFunc = wrap(myFunc, beforeExecute, afterExecute);

However, I don’t have an implementation of the required wrap function. Is there anything that already exists in jQuery like this (I’ve had a good look through the docs but cannot see anything)? Alternatively does anybody know of a good implementation of this because I suspect that there are a bunch of edge cases that I’ll miss if I try to write it myself?

(BTW – the reason for this is to do some automatic instrumentation of functions because we do a lot of work on closed devices where Javascript profilers etc. are not available. If there’s a better way than this then I’d appreciate answers along those lines too.)

Answer 1

Here’s a wrap function which will call the before and after functions with the exact same arguments and, if supplied, the same value for this:

var wrap = function (functionToWrap, before, after, thisObject) {
    return function () {
        var args = Array.prototype.slice.call(arguments),
            result;
        if (before) before.apply(thisObject || this, args);
        result = functionToWrap.apply(thisObject || this, args);
        if (after) after.apply(thisObject || this, args);
        return result;
    };
};

myFunc = wrap(myFunc, beforeExecute, afterExecute);