The use of the semicolon in front of;function($,undefined) in jQuery_jquery

;(function($){$.extend($.fn...

Generally, there is a semicolon in front of some JQuery functions. Adding a semicolon in front can be used for many purposes:

1. Prevent syntax errors from occurring in high compression after multiple files are integrated into one file.

2. This is an anonymous function. Generally, js libraries use this self-executing anonymous function to protect internal variables (function(){})().

3. Because undefined is an attribute of window, after it is declared as a local variable, if there are variables in the function that are compared with undefined, the program does not need to search for undefined to window, which can improve program performance.