What does this structure in Javascript mean?

Im learning javascript and I just dont understand what this javascri开发者_JAVA百科pt syntax actually means...

Comment = function () {

}

I know that in this context we use it to define an object but what is the stucture called where can I read about it?

This statement is a function expression.

It creates an anonymous function and assigns it to the (global) variable Comment.

It is similar to function Comment() {} except one difference: It does not have a name so debuggers might just display ? instead of a function name and more important, the function is defined when the line containing the definition is executed while function declarations are "executed" before the other code is executed.

Example: http://jsfiddle.net/ThiefMaster/nVrep/

You are defining a function named Comment, this is equivalent to:

function Comment() {

}

Because there is now var keyword like here:

var Comment = function() {}

the Comment variable will be added to global object called window, so it is equivalent to:

window.Comment = function() {

}

Also, by convention, capitalized function names are used for so called constructors:

var comment = new Comment();

That is a function operator (as opposed to a function statement or function constructor)