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I found that sometimes the script don't run properly when I add script tag in the head section. But when I add script right before the ending tag of body it works fine.

What is the difference between adding script in head tag
OR
on just before ending body tag
OR
right after the control?

I found this issue very often when I use JQuery..

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Although Jalayn's answer is the most likely cause, we can't really speculate what's wrong with your scripts unless you show us your actual code. If you decide to do so, please post the question on Stack Overflow, technical questions are off topic for Programmers. – Yannis Rizos♦ Jun 15 '12 at 6:09
2  
Why was this closed? – Oliver Weiler Jun 15 '12 at 8:10
@OliverWeiler Because it's off-topic. – FishBasketGordo Jun 15 '12 at 11:40

closed as not a real question by Yannis Rizos♦ Jun 15 '12 at 6:09

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.

1 Answer

up vote 4 down vote accepted

It is very simple in fact. If your script is not bound to a document ready event, it will fire up instantly, that is, when the page is being loaded, NOT when it has loaded. What it means is that the HTML controls/tags below your script tag have not been added yet to the DOM. And as such, attempting to interact with them will not work.

If you place your script tags after the control/tag is created, the tag is in the DOM and jquery "sees" it.

For these reasons it is always recommended to bind your javascript to a document "ready" function, so that it will fire only when the DOM tree has been properly and completely instantiated.

For a more detailed explanation, you might be interested in reading this post, about the "ready" function.

Also, check out http://stackoverflow.com/q/1307929/866172 if you are interested in knowing how the web page is loaded by the browser (hint: top to bottom, or "as it is seen"). The advice in the top answer is to place the script tag at the end of the document, which makes sense, but if you are using jquery, whatever the place of your script tag is, if you wrap your code in a "ready" function you won't have any problems.

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