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What does this mean? (function (x,y)){…}){a,b); in JavaScript

Please anyone explain and give example about the Javascript below, I can’t find any document that explain about this:

(function([arg, arg ...]) {

    //javascript code here

})([str, str ...]);

I’m asking this question because I see in the Google also Facebook javascript code, most of the them using this syntax.

Answer 1

What’s happening is, an anonymous function expression is defined (in parentheses) –

(function([arg, arg ...]) {

    //javascript code here

})

The function is then immediately called using the () at the end of the function, just as as you’d call a normal function var result = someFunction(). So , for example –

(function() {
    alert('Called by "()" at end of function');
})()

You can also pass arguments to the anoymous function, via the parentheses –

(function(username) {
    alert('Called by "()" at end of function. Hello ' + username + '!');
})('Dave')