Why need to use semicolon before defining a function? [duplicate]

问题

This question already has answers here:

What does the leading semicolon in JavaScript libraries do? (6 answers)

What's the purpose of starting semi colon at beginning of JavaScript? [duplicate] (2 answers)

Closed 6 years ago.

I've seen some strange ; at the beginning of a function in some jQuery plugins source code like this:

;(function ($) {.....

Can someone explain why they need to use ; in this case?

回答1:

This semicolon will help you to properly concatenate a new code into a file when the current existed code in this file does not include a ; at the end.

For example:

(function() {

})()  // <--- No semicolon

//  Added semicolon to prevent unexpected laziness result from previous code    
;(function ($) {

})();

Without the semicolon, the second () would have been interpreted as a function call, and will tried to call the return result of the first function

回答2:

This is just to make sure to terminate any previous instruction.

the semi colon before function invocation is a safety net against concatenated scripts and/or other plugins which may not be closed properly.

https://github.com/shichuan/javascript-patterns/blob/master/jquery-plugin-patterns/extend.html

来源：https://stackoverflow.com/questions/16319510/why-need-to-use-semicolon-before-defining-a-function