When should I use jQuery's document.ready function?

Question

I was told to use document.ready when I first started to use Javascript/jQuery but I never really learned why.

Might someone provide some basic guidelines on when it makes sense to wrap javascript/jquery code inside jQuery's document.ready?

Some topics I'm interested in:

jQuery's .on() method: I use the .on() method for AJAX quite a bit (typically on dynamically created DOM elements). Should the .on() click handlers always be inside document.ready?
Performance: Is it more performant to keep various javascript/jQuery objects inside or outside document.ready (also, is the performance difference significant?)?
Object scope: AJAX-loaded pages can't access objects that were inside the prior page's document.ready, correct? They can only access objects which were outside document.ready (i.e., truly "global" objects)?

Update: To follow a best practice, all my javascript (the jQuery library and my app's code) is at the bottom of my HTML page and I'm using the defer attribute on the jQuery-containing scripts on my AJAX-loaded pages so that I can access the jQuery library on these pages.

Because if the DOM is not ready, you may get unexpected results, that's all. — Robert Harvey, Oct 25 '12 at 05:40
2.- Well i use **outside** just to debug and can to call some var/function by console, — jd_7, Oct 25 '12 at 05:49
@RobertHarvey what kind of "unexpected" results? can you provide an example? — tim peterson, Oct 25 '12 at 06:06
You try to modify an element or attribute that hasn't made it to the DOM yet. — Robert Harvey, Oct 25 '12 at 14:41

score 149 · Accepted Answer · edited Jul 22 '19 at 18:13

149

In simple words,

$(document).ready is an event which fires up when document is ready.

Suppose you have placed your jQuery code in head section and trying to access a dom element (an anchor, an img etc), you will not be able to access it because html is interpreted from top to bottom and your html elements are not present when your jQuery code runs.

To overcome this problem, we place every jQuery/javascript code (which uses DOM) inside $(document).ready function which gets called when all the dom elements can be accessed.

And this is the reason, when you place your jQuery code at the bottom (after all dom elements, just before </body>) , there is no need for $(document).ready

There is no need to place on method inside $(document).ready only when you use on method on document because of the same reason I explained above.

    //No need to be put inside $(document).ready
    $(document).on('click','a',function () {
    })

    // Need to be put inside $(document).ready if placed inside <head></head>
    $('.container').on('click','a',function () {
    });

EDIT

From comments,

$(document).ready does not wait for images or scripts. Thats the big difference between $(document).ready and $(document).load
Only code that accesses the DOM should be in ready handler. If it's a plugin, it shouldn't be in the ready event.

edited Jul 22 '19 at 18:13

Soner from The Ottoman Empire

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answered Oct 25 '12 at 05:46

Jashwant

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@Dipaks Yes, why not ? We are just very used to use `$(document).ready`. See [this](http://jsfiddle.net/GrvwX/) – Jashwant Oct 25 '12 at 05:54
As long as you load jQuery in the `head` and you're scripts after the elements being manipulated, `document.ready` is not needed. Images are a special case though... – elclanrs Oct 25 '12 at 05:54
@elclanrs See my updated question. I'm loading jQuery at the bottom of my HTML page with my app-specific code right after that. – tim peterson Oct 25 '12 at 06:14
@Jashwant how about performance differences of dom.ready vs. not? Are those relevant? – tim peterson Oct 25 '12 at 06:15
I dont think there's much of a performance difference (there were performance degradation in case of `live` but `on` works differently). You can always use [jsperf](http://jsperf.com). If you are putting jQuery code at bottom, why using `dom.ready` ? If not more, it at least increases a functional call. – Jashwant Oct 25 '12 at 07:05
1

We don't put all `jQuery` code in the ready handler. Only code that accesses the DOM. If it's a plugin, it shouldn't be in the `ready` event – Ruan Mendes Apr 08 '13 at 18:40
very nice explained bro...+1 – Dinesh Oct 17 '14 at 04:55
THAT is why we love this site. Thank you. 1++ :) – Colin R. Turner Jul 03 '15 at 10:28
I'm not sure am I right, but when you put event inside of document.ready, it will fail. Is this real? (please, someone, protect this question, too much of +1 comments...) – Feb 27 '17 at 17:09
upvoted! if your script is at the bottom of body, why do you need document.ready? – PirateApp Aug 22 '18 at 10:05
You don't need `document.ready` if you script is placed after the DOM elements it is going to use. If it is at the bottom of body, you don't need `document.ready` at all. – Jashwant Aug 22 '18 at 10:34

score 7 · Answer 2 · answered Oct 25 '12 at 05:51

Answers:

jQuery's .on() method: I use the .on() method for AJAX quite a bit (dynamically creating DOM elements). Should the .on() click handlers always be inside document.ready?

No, not always. If you load your JS in the document head you will need to. If you are creating the elements after the page loads via AJAX, you will need to. You will not need to if the script is below the html element you are adding a handler too.

Performance: Is it more performant to keep various javascript/jQuery objects inside or outside document.ready (also, is the performance difference significant?)?

It depends. It will take the same amount of time to attach the handlers, it just depends if you want it to happen immediately as the page is loading or if you want it to wait until the entire doc is loaded. So it will depend what other things you are doing on the page.

Object scope: AJAX-loaded pages can't access objects that were inside the prior page's document.ready, correct? They can only access objects which were outside document.ready (i.e., truly "global" objects)?

It's essentially it's own function so it can only access vars declared at a global scope (outside/above all functions) or with window.myvarname = '';

score 6 · Answer 3 · edited Feb 18 '13 at 00:50

Before you can safely use jQuery you need to ensure that the page is in a state where it's ready to be manipulated. With jQuery, we accomplish this by putting our code in a function, and then passing that function to $(document).ready(). The function we pass can just be an anonymous function.

$(document).ready(function() {  
    console.log('ready!');  
});

This will run the function that we pass to .ready() once the document is ready. What's going on here? We're using $(document) to create a jQuery object from our page's document, and then calling the .ready() function on that object, passing it the function we want to execute.

Since this is something you'll find yourself doing a lot, there's a shorthand method for this if you prefer — the $() function does double duty as an alias for $(document).ready() if you pass it a function:

$(function() {  
    console.log('ready!');  
});

This is a good reading: Jquery Fundamentals

Not to be confused with `(function($){ })(jQuery);` which wraps your code so that $ is jQuery inside that closure — John Magnolia, Nov 05 '14 at 10:15

score 3 · Answer 4 · answered Oct 25 '12 at 05:44

3

.ready() - Specify a function to execute when the DOM is fully loaded.

$(document).ready(function() {
  // Handler for .ready() called.
});

Here is a List of all jQuery Methods

Read on Introducing $(document).ready()

answered Oct 25 '12 at 05:44

Dipak

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elclanrs · Answer 5 · 2012-10-25T05:52:34.217

To be realistic, document.ready is not needed for anything else than manipulating the DOM accurately and it's not always needed or the best option. What I mean is that when you develop a large jQuery plugin for example you hardly use it throughout the code because you're trying to keep it DRY, so you abstract as much as possible in methods that manipulate the DOM but are meant to be invoked later on. When all your code is tightly integrated the only method exposed in document.ready is usually init where all the DOM magic happens. Hope this answers your question.

score 1 · Answer 6 · answered Oct 25 '12 at 05:47

You should bind all actions in document.ready, because you should wait till the document is fully loaded.

But, you should create functions for all actions and call them from within the document.ready. When you create functions (your global objects), call them whenever you want. So once your new data is loaded and new elements created, call those functions again.

These functions are the ones where you've bound the events and action items.

$(document).ready(function(){
bindelement1();
bindelement2();
});

function bindelement1(){
$('el1').on('click',function...);
//you might make an ajax call here, then under complete of the AJAX, call this function or any other function again
}

function bindelement2(){
$('el2').on('click',function...);
}

score 0 · Answer 7 · answered Sep 25 '17 at 06:37

I appended a link to a div and wanted to do some tasks on the click. I added the code below the appended element in the DOM but it did not work. Here is the code:

<div id="advance-search">
   Some other DOM elements
   <!-- Here I wanted to apppend the link as <a href="javascript:;" id="reset-adv-srch"><span class="bold">x</span> Clear all</a>-->
</div>

<script>
  $("#advance-search #reset-adv-srch").on("click", function (){
     alert('Link Clicked');``
  });
</script>

It did not work. Then I placed the jQuery code inside $(document).ready and it worked perfectly. Here it is.

$(document).ready(function(e) {
    $("#advance-search #reset-adv-srch").on("click", function (){
        alert('Link Clicked');
    });
});

score -2 · Answer 8 · answered Jan 19 '15 at 08:35

he ready event occurs when the DOM (document object model) has been loaded.

Because this event occurs after the document is ready, it is a good place to have all other jQuery events and functions. Like in the example above.

The ready() method specifies what happens when a ready event occurs.

Tip: The ready() method should not be used together with .

When should I use jQuery's document.ready function?

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