What's the purpose (if any) of "javascript:" in event handler tags?

Question

I've been making a concerted effort to improve my javascript skills lately by reading as much javascript code as I can. In doing this I've sometimes seen the javascript: prefix appended to the front of event handler attributes in HTML element tags. What's the purpose of this prefix? Basically, is there any appreciable difference between:

onchange="javascript: myFunction(this)"

and

onchange="myFunction(this)"

?

Answer 1

Probably nothing in your example. My understanding is that javascript: is for anchor tags (in place of an actual href). You'd use it so that your script can execute when the user clicks the link, but without initiating a navigation back to the page (which a blank href coupled with an onclick will do).

For example:

<a href="javascript:someFunction();">Blah</a>

Rather than:

<a href="" onclick="someFunction();">Blah</a>

Answer 2

It should not be used in event handlers (though most browsers work defensively, and will not punish you). I would also argue that it should not be used in the href attribute of an anchor. If a browser supports javascript, it will use the properly defined event handler. If a browser does not, a javascript: link will appear broken. IMO, it is better to point them to a page explaining that they need to enable javascript to use that functionality, or better yet a non-javascript required version of the functionality. So, something like:

<a href="non-ajax.html" onclick="niftyAjax(); return false;">Ajax me</a>

Edit: Thought of a good reason to use javascript:. Bookmarklets. For instance, this one sends you to google reader to view the rss feeds for a page:

var b=document.body;
if(b&&!document.xmlVersion){
  void(z=document.createElement('script'));
  void(z.src='http://www.google.com/reader/ui/subscribe-bookmarklet.js');
  void(b.appendChild(z));
}else{
  location='http://www.google.com/reader/view/feed/'+encodeURIComponent(location.href)
}

To have a user easily add this Bookmarklet, you would format it like so:

<a href="javascript:var%20b=document.body;if(b&&!document.xmlVersion){void(z=document.createElement('script'));void(z.src='http://www.google.com/reader/ui/subscribe-bookmarklet.js');void(b.appendChild(z));}else{location='http://www.google.com/reader/view/feed/'+encodeURIComponent(location.href)}">Drag this to your bookmarks, or right click and bookmark it!</a>