jQuery - Function Parameters

Question

I read the following, but still want to discuss.... Meaning of evt = (evt) ? evt : window.event

//Would evt need to be passed because it is not used in the function??? --- Trying to get my mind wrapped around this jQuery stuff.

A)

$('#' + _ids.btnPrintServiceCode).on('click', function (evt) {
        alert('Hello World')
    });

OR

B)

$('#' + _ids.btnPrintServiceCode).on('click', function () {
        alert('Hello World')
    });

Side note: You can call `evt` whatever you want. You can call it `function(IAmMoojjoo)` and it will still work: [demo](http://jsfiddle.net/dirtyd77/sZEuC/1/). Also start using [`console.log()`](http://stackoverflow.com/questions/4743730/what-is-console-log-and-how-do-i-use-it) rather than `alert()`; it is a better tool for debugging. — Dom, Apr 30 '13 at 18:10

score 3 · Accepted Answer · edited Apr 06 '22 at 20:17

3

You don't need to pass the evt if it is not used, it is optional. However having it won't create an issue.

You basically pass evt if you need to listen to the event. Say you want to prevent the default behaviour of some elements, so you need evt here.

HTML

<a href="#"></a>

jQuery

$('a').on('click', function (evt) {
    evt.preventDefault(); // this will prevent the default behaviour of that element
    alert('Hello World');
});

$('input').keyup(function(e){ //here we need to pass e as we are using e to get the keyCode that was pressed
   if(e.keyCode == 8 )
   {
        alert('test');
    }
});

edited Apr 06 '22 at 20:17

halfer

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answered Apr 30 '13 at 18:01

bipen

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So does it hurt anything to have it. I am picking up work from another developer? – Moojjoo Apr 30 '13 at 18:02
1

The `event` object is *always* passed to your function. You don't have to add a parameter for it. – gen_Eric Apr 30 '13 at 18:02
So why would it be written like A)? Looking to understand this better. Thank you ahead of time. – Moojjoo Apr 30 '13 at 18:03

score 1 · Answer 2 · answered Apr 30 '13 at 18:11

Think of it this way. Lets say i have this function:

function foo (bar) {
    alert("worky");
}
foo("foobar"); // worky

Since inside the function i'm never actually using bar, i can simplify the function by removing bar from the parameter list.

function foo () {
    alert("worky");
}
foo("foobar"); // worky

both will have the same result. The same is true with your event binding. Since you are never using evt, there is no reason for you to pass it to the function, however it won't hurt anything if you do anyway.

If the previous developer always passed evt to event handler callbacks, you should continue to do so to keep the code consistent, but that's entirely up to you.

Awesome, that did it... Thanks ---- LIGHTBULB... DING DING DING — Moojjoo, Apr 30 '13 at 18:19

jQuery - Function Parameters

2 Answers2