iife-variations.js

// Want to learn more about Immediately Invoked Function Expressions? Read
// this article first:
// 
// http://benalman.com/news/2010/11/immediately-invoked-function-expression/

// Parens are used to tell the parser that it's a function expression,
// not a function declaration. If you don't explicitly tell the parser to
// expect an expression, it will throw a SyntaxError exception because it
// sees a function declaration without a name specified.

(function(){ /* code */ })() // I've been using this one
(function(){ /* code */ }()) // Crockford recommends this one

// If you don't care about the possible performance overhead of performing
// type coercion on the function's return value, you can save a byte by
// prefixing the function with a unary operator.

!function(){ /* code */ }()
~function(){ /* code */ }()
-function(){ /* code */ }()
+function(){ /* code */ }()

// Because the point of the parens or coercing operators is just to tell
// the parser to expect a function expression and not a declaration, they
// can be omitted when it already expects an expression.

var i = function(){ return 10; }();
condition && function(){ /* code */ }();

// Here's another variation, from @kuvos - I'm not sure of the performance
// implications of using the `new` keyword, but it works.
// http://twitter.com/kuvos/status/18209252090847232

new function(){ /* code */ }
new function(){ /* code */ }() // Only need parens if passing arguments