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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:
.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?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.
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The ready() method is used to make a function available after the document is loaded. Whatever code you write inside the $(document ). ready() method will run once the page DOM is ready to execute JavaScript code.
The . ready() method offers a way to run JavaScript code as soon as the page's Document Object Model (DOM) becomes safe to manipulate. This will often be a good time to perform tasks that are needed before the user views or interacts with the page, for example to add event handlers and initialize plugins.
The document ready event signals that the DOM of the page is now ready, so you can manipulate it without worrying that parts of the DOM has not yet been created. The document ready event fires before all images etc. are loaded, but after the whole DOM itself is ready.
So technically they are both the same. Not major difference between these two declaration. They used based on weather you use JavaScript then you should use $(document). ready declaration in other case you use jQuery library which is a part of JavaScript then you should use $(function) declaration.
In simple words,
$(document).readyis an event which fires up whendocumentis 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.
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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 = '';
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