Why is it bad practice to use links with the javascript: "protocol"?

Question

In the 1990s, there was a fashion to put Javascript code directly into <a> href attributes, like this:

<a href="javascript:alert('Hello world!')">Press me!</a> 

And then suddenly I stopped to see it. They were all replaced by things like:

<a href="#" onclick="alert('Hello world!')">Press me!</a> 

For a link whose sole purpose is to trigger Javascript code, and has no real href target, why is it encouraged to use the onclick property instead of the href property?

Answer 1

The execution context is different, to see this, try these links instead:

<a href="javascript:alert(this.tagName)">Press me!</a> <!-- result: undefined --> <a href="#" onclick="alert(this.tagName)">Press me!</a> <!-- result: A --> 

javascript: is executed in the global context, not as a method of the element, which is usually want you want. In most cases you're doing something with or in relation to the element you acted on, better to execute it in that context.

Also, it's just much cleaner, though I wouldn't use in-line script at all. Check out any framework for handling these things in a much cleaner way. Example in jQuery:

$('a').click(function() { alert(this.tagName); }); 

Answer 2

Actually, both methods are considered obsolete. Developers are instead encouraged to separate all JavaScript in an external JS file in order to separate logic and code from genuine markup

• http://www.alistapart.com/articles/behavioralseparation
• http://en.wikipedia.org/wiki/Unobtrusive_JavaScript

The reason for this is that it creates code that is easier to maintain and debug, and it also promotes web standards and accessibility. Think of it like this: Looking at your example, what if you had hundreds of links like that on a page and needed to change out the alert behavior for some other function using external JS references, you'd only need to change a single event binding in one JS file as opposed to copying and pasting a bunch of code over and over again or doing a find-and-replace.