Three ways to create a function:
1.Declarative function: parsed when the javascript application is first loaded.
2.Anonymous function or function constructor:parsed each time it‘s accessed.
3.Function literal or function expression:used in place-such as a callback function.Aslo parsed once
when the javascript application is loaded.can also anonymous.
原文：http://www.cnblogs.com/sky-zhao/p/5056141.html