Unrecognized function syntax: class.event = (function(arg){[stuff]})(arg?);

[pstephan1187]

I was working on a tutorial for some ajax uploading stuff and I ran across a new function syntax I don't recognize. I am not a Javascript pro, but I am not a newbie either. here is the code I am working on:

		function handleFileSelect(e){
			var files = e.target.files;
			var output = [];
			for(var i=0,f;f=files[i];i++){
				if(f.type.match('image.*')){
					var reader = new FileReader();
					
					reader.onload = (function(theFile){
						return function(e){
							var span = document.createElement('span');
							span.innerHTML = ['<img class="thumb" src="',e.target.result,'" title="',theFile.nbame,'" />'].join('');
							document.getElementById('list').insertBefore(span,null);
						};
					})(f);
					
					reader.readAsDataURL(f);
				}
			}
			document.getElementById('list').innerHTML = '<ul>'+output.join('')+'</ul>';
		}
		document.getElementById('files').addEventListener('change',handleFileSelect,false);

To be a little more clear, the code in question is that is the very middle. The syntax I don't understand is:

class.event = (function(arguments){
     //stuff you put in a function...
})(more Arguments?);

I tried to customize a simple one to learn for myself and I wrote this:

var a = 'A';
var b = 'B';

test = (function(t){
     alert(t);
     alert(b);
})(b);

test(a);

The browser would alert 'B' and that's it. The console would tell me that 'test is not a function.' OK, so I am confused.

The topmost code works. What I am wondering is what the syntax is called for creating a function (or event listener?) that way, and how it works. Although if I new what it was called I could just google how it works.

[DaveyErwin]

http://en.wikibooks.org/wiki/JavaScr...mous_Functions

[pstephan1187]

Exactly what I needed. Thank you!

[DaveyErwin]

var a = 'A';
var b = 'B';

test = (function(t){
     alert(t);
     alert(b);
})(b);


alert(test)
//test(a);

Test will equal the return value
of the anonymous function, in
this case there is no reurn value
so test is undefined.