How to extend JavaScript functions

extending_functions.js

Array.prototype.join = (function(_super) {

    // return our new `join()` function
    return function() {
        console.log("Hey, you called join!");
        return _super.apply(this, arguments);
    };
       // Pass control back to the original join()
       // by using .apply on `_super`

})(Array.prototype.join);
//                            
// Pass the original function into our
// immediately invoked function as `_super`
// which remains available to our new
// function thanks to JavaScript Closures.