I'm curious what situations exactly require the use of jquery's $(document).ready() or prototype's dom:loaded or any other variant of a handler for this event.
In all the browsers i've tested, it's entirely acceptable to begin interacting with html elements and the DOM immediately after the closing tag. (e.g.
<div id="myID">
My Div
</div>
<script type="text/javascript">
$('#myID').initializeElement();
</script>
So at this point i'm wondering whether $(document).ready() is merely there to reduce the thinking involved in writing javascript code that runs during page load. In the case of using $(document).ready() there is regularly rendering issues such as popping and 'artifacts' between the browser first starting to draw the page and the javascript actually executing when the page is 'ready'.
Are there any scenarios where $(document).ready() is required?
Are there any reasons I shouldn't be writing initialization scripts as demonstrated?
I'm curious what situations exactly require the use of jquery's $(document).ready() or prototype's dom:loaded or any other variant of a handler for this event.
In all the browsers i've tested, it's entirely acceptable to begin interacting with html elements and the DOM immediately after the closing tag. (e.g.
<div id="myID">
My Div
</div>
<script type="text/javascript">
$('#myID').initializeElement();
</script>
So at this point i'm wondering whether $(document).ready() is merely there to reduce the thinking involved in writing javascript code that runs during page load. In the case of using $(document).ready() there is regularly rendering issues such as popping and 'artifacts' between the browser first starting to draw the page and the javascript actually executing when the page is 'ready'.
Are there any scenarios where $(document).ready() is required?
Are there any reasons I shouldn't be writing initialization scripts as demonstrated?
Share Improve this question edited Jun 14, 2013 at 9:55 Adil Shaikh 44.7k17 gold badges95 silver badges112 bronze badges asked May 15, 2011 at 0:53 hannasmhannasm 2,0414 gold badges17 silver badges25 bronze badges 1- possible duplicate of jQuery: Why use document.ready if external JS at bottom of page? – Ciro Santilli OurBigBook.com Commented Feb 6, 2014 at 17:21
3 Answers
Reset to default 10The main reason is external files that are included in the head. When you include a file in your <head> it gets run immediately. This means if the JavaScript interacts with the DOM it needs to be wrapped in Dom Ready.
It's also needed for unobtrusive JavaScript and separations of concerns. Ideally your JavaScript and HTML are in separate files. If you follow this you will not have any in-line script tags in your HTML at all.
The second is to defend yourself against obscure browser bugs when you make mistakes. There are cases where it's not save to go and manipulate DOM elements immediately afterwards. (I'm looking at you IE6!)
The third reason is to keep your code clean.
Mixing script tags into your HTML makes spaghetti code.
some HTML
<script> ... </script>
some HTML
<script> ... </script>
some HTML
<script> ... </script>
some HTML
<script> ... </script>
some HTML
<script> ... </script>
some HTML
<script> ... </script>
some HTML
<script> ... </script>
We have code about ten times worse then that. It's a right pain to read / maintain
In the case of external scripts $(document).ready() could be the only option. As for inline script it is a little different.
According to HTML 4.01 standard it seems a little ambiguous whether or not the initialization technique shown above is legal:
http://www.w3.org/TR/html401/interact/scripts.html#h-18.2.4
Scripts that are executed when a document is loaded may be able to modify the document's contents dynamically. The ability to do so depends on the scripting language itself (e.g., the "document.write" statement in the HTML object model supported by some vendors).
HTML documents are constrained to conform to the HTML DTD both before and after processing any SCRIPT elements.
In the HTML 5 draft it seems very clear that this practice is fully supported:
http://www.w3.org/TR/html5/scripting-1.html#scripting-1
The following sample shows how a script element can be used to define a function that is then used by other parts of the document. It also shows how a script element can be used to invoke script while the document is being parsed, in this case to initialize the form's output.
<script>
function calculate(form) {
var price = 52000;
if (form.elements.brakes.checked)
price += 1000;
if (form.elements.radio.checked)
price += 2500;
if (form.elements.turbo.checked)
price += 5000;
if (form.elements.sticker.checked)
price += 250;
form.elements.result.value = price;
}
</script>
<form name="pricecalc" onsubmit="return false">
<fieldset>
<legend>Work out the price of your car</legend>
<p>Base cost: £52000.</p>
<p>Select additional options:</p>
<ul onchange="calculate(form)">
<li><label><input type=checkbox name=brakes> Ceramic brakes (£1000)</label></li>
<li><label><input type=checkbox name=radio> Satellite radio (£2500)</label></li>
<li><label><input type=checkbox name=turbo> Turbo charger (£5000)</label></li>
<li><label><input type=checkbox name=sticker> "XZ" sticker (£250)</label></li>
</ul>
<p>Total: £<output name=result></output></p>
</fieldset>
<script>
calculate(document.forms.pricecalc);
</script>
</form>
Everything inside it will load as soon as the DOM is loaded and before the page contents are loaded.
The $(document).ready() function has a ton of advantages over other ways of getting events to work. First of all, you don't have to put any "behavioral" markup in the HTML
With $(document).ready(), you can get your events to load or fire or whatever you want them to do before the window loads.