向JavaScript中的预定义事件添加功能

Question

Is there a way in JavaScript that I can override an event, but still call the original event's code? I basically want to add a single line of code to the end. So for example:

Original function

function DropDownList_OnFocus(a, b) {
    // Original Code
}

What I'd need

function DropDownList_OnFocus(a, b) {
    // Original Code
    // New Code        
}

Answer 1

Event handlers always execute sequentially in the order they were bound.

So You can simply add another event handler for the same event on the same element and put more/remaining code in the second event handler.

Answer 2

I've managed to get it working using the following:

var base = DropDownList.OnFocus;
var DropDownOnFocusOverride = (function () {
    return function () {
        base();
        // Additional Code
    }
});

DropDownList.OnFocus = DropDownOnFocusOverride();