gistfile1.js

Function.prototype.before = function(methodName, newFunc) {
	if(typeof this == "function") {
		var oldFunc = this.prototype[methodName];
		this.prototype[methodName] = function() {
			newFunc.apply(this, arguments);
			return oldFunc.apply(this, arguments);
		};
	} else if(typeof this == "object") {
		var oldFunc = instance[methodName];
			instance[methodName] = function() {
				newFunc.apply(instance, arguments);
				return oldFunc.apply(instance, arguments);
			};
	}
	
};

var SomeObject = function() {
	this.instanceMethod = function() {
		console.log("instance method");
	}
};
SomeObject.prototype.someMethod = function(testParam) {
	console.log("someMethod was called with: " + testParam);
	return "someVal";
};

//create new SomeObject
var obj = new SomeObject();

//set before rule
SomeObject.before("someMethod", function(testParam) {
	console.log("This is executed before someMethod is executed, param is: " + testParam);
});

SomeObject.before(obj, "instanceMethod", function() {
	console.log("executed before instance method");
});

//call someMethod
obj.someMethod("hello");
obj.instanceMethod();