Problems that are encountered in JavaScript

Question one: Why in JS in the function ($) preceded by a semicolon source

1, prevent the integration of multiple files into a file, high compression syntax error occurs.

2, this is an anonymous function, the General JS Library uses this self-executing anonymous function to protect internal variables

(function() {}) ()

3, because undefined is the property of window, declared as a local variable, in the function if there are variables and undefined for comparison, the program can not search undefined to window, can improve program performance

Problems that are encountered in JavaScript