CODEWITHSUNDEEP
javascriptjquery
Kshitiz Sharma
Kshitiz Sharma

Reputation: 18607

Why do I need to wrap my JQuery code in a function literal?

I have following code that works - 

$(function(){
    $('#testbutton').click(function(){
        var checkedValue = $('[name="someRadioGroup"]:radio:checked').val();
        $('#result').html('The radio element with value <tt>' + checkedValue + '</tt> is checked');
    });
});

I understand that $('#testbutton') fetches the HTML element with id testbutton and assigns an event handler to it.

But I don't understand why I need to put that code inside a function literal?

If I remove the $(function(){ (and the corresponding }); ) it does not work.

However other code can work without being wrapped in a function literal. Example - alert('Hi there')

What is the difference? Why does alert work but the event assignment statement does not?

Upvotes: 4

Views: 1135

Answers (3)

gray state is coming
gray state is coming

Reputation: 2107

It is not a requirement.

You are putting your code in an event handler that is invoked when the DOM is ready.

If you don't put your code in a DOM ready handler, and if your code performs DOM selection, you need to find some other way to to make sure the DOM is ready before it runs.

If your code doesn't perform DOM selection, then it's not needed. That's why your alert() works, because it doesn't need to fetch any elements.

An alternative is this.

<body>
   <button id="testbutton">click</button>
   <div id="result"></div>

   <script type="text/javascript" src="/your/script.js"></script>
</body>

This places your code below all the elements on the page, so they are certain to be available when your code runs.

Another alternative is to use a window.onload handler.

window.onload = function() {
    // your code
};

or using jQuery.

$(window).on("load", function() {
    // your code
});

This is similar to the DOM ready handler, except that it waits for all resource, like images, to be loaded.

Upvotes: 2

Shreedhar
Shreedhar

Reputation: 5640

At the most basic level, something of the form (function(){...})() is a function literal that is executed immediately. What this means is that you have defined a function and you are calling it immediately.

This form is useful for information hiding and encapsulation since anything you define inside that function remains local to that function and inaccessible from the outside world (unless you specifically expose it - usually via a returned object literal).

A variation of this basic form is what you see in jQuery plugins (or in this module pattern in general). Since you are defining a function literal, it doesn't have access to anything from the outside world unless you explicitly pass in the information. Hence:

(function($) {
  ...
})(jQuery);

Which means you're passing in a reference to the actual jQuery object, but it's known as $ within the scope of the function literal.

Upvotes: 0

Kevin B
Kevin B

Reputation: 95017

$(function(){...}); is shorthand for $(document).ready(function(){...});. The purpose of it is to not run your code until the elements that you intend to work with exist in the DOM (which generally is after the document is ready.)

Upvotes: 7

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