Question

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What is the purpose of wrapping whole Javascript files in anonymous functions like “(function(){ … })()”?

I came across a JS file that can be summarized to the code below:

   (function(window){
              // some codes here
                    })(window);

I wonder what this block of code means? Has the window special meanings, or it is just a parameter? What are the differences between the two “window” we see in the brackets?

Since this function does not have a name, I assume it is an anonymous function, so is it only invoked once? When is it invoked?

Answer 1

As far your questions regarding window, the window in parentheses at the bottom is a reference to the global window object. The first window is just a name for a parameter. But in this instance it refers to the global window object since you’re using an anonymous self-invoked function. You could call it monkeys and it wouldn’t make a difference (of course, you’d have to use monkeys within the body of the anonymous function then, to refer to the parameter). So now, you now have a reference to the global window object within your function.

Yes, the function is invoked once and it is invoked as soon as it is defined. This is because it is a self-invoked anonymous function.