Possible Duplicate:
JavaScript: var functionName = function() {} vs function functionName() {}
Declaring functions in JavaScript
I've seen 2 different syntaxes for defining functions in javascript:
function f() {
...
}
As well as
var f = function() {
...
};
What's the difference between these? Is one of them deprecated?
Neither are deprecated, and both will work. The difference here is that one is a named function ( function f() ) while the other is a variable equal to a function ( var f = function() ).
You have to be careful when setting variables equal to functions. This will work:
var f = function(n) { console.log(n); };
f(3); // logs 3
But this will break, since the variable is defined after the call to it.
f(3); // what is f? breaks.
var f = function(n) { console.log(n); };
But normal functions work fine.
function abc(n) { console.log(n); }
abc(3); // logs 3
xyz(5); // logs 5
function xyz(n) { console.log(n); }
This is because the code is analysed before execution, and all functions are available to call. But setting a var equal to a function is like setting a var to anything else. The order of when it happens is important.
Now for some more confusing stuff...
There are also 'self-executing' anonymous functions. They go by a variety of names. The most common way to do it looks something like this:
(function() {
// code in here will execute right away
// since the () at the end executes this (function(){})
})();
There is also an arguably better version.
!function() {
// again, the tailing () will execute this
}();
Check out this Stack Overflow post for more on anonymous functions.
(function foo() {...}()), or named functions assigned to a variable: var foo = function bar() {...};. The actual noteworthy difference is that one is a function declaration which always has to be named, whereas a function expression can either be named or anonymous.
(function foo() {...}()) are interesting since you can call foo from within itself, but not outside. Even when writing it as !function foo() {...}();.
