Why there is semicolon at the start of a JavaScript function?

Very often while reviewing the code for my team, I will come across a semicolon at the start of JavaScript function as show below

;
(function () {
    'use strict';

...and I often wondered what purpose it served.

Guess what. It is an insurance to make sure your script works fine when all other scripts are merged together; 

The leading ; in front of immediately-invoked function expressions (iffe) is there to prevent errors when appending the file during concatenation to a file containing an expression not properly terminated with a ;.

So there you go. Now you know what that little semicolon is doing there in your code.