How to override JavaScript/jQuery functions and events?

Below code snippet show that with the help of .off() function we can override events in jquery

$(document).off('event', 'selector').on('event', 'selector', function() {
	// Your code
});

Suppose you have a predefined js function helloWorld

function helloWorld (argument) {
	alert(argument);
}

Now, if you want to override this function then

var origHelloWorld = window.helloWorld;
window.helloWorld = function(argument) {
    	//your code
    	origHelloWorld(argument); 	// after your code if you want to call original function 
}