A function in JavaScript looks like the following:
(function(){...})()
A library in JavaScript shows a function, which begins with a semicolon, for example:
;(function ) { }
The semicolon allows to safely concatenate several JS files into one. This is to serve it faster as one HTTP request.
A leading semicolon can also be to protect from preceding code, which may have been improperly closed. A semicolon will definitely prevent this from happening.