Question

I was reading the jQuery source and I was wondering why the entire source file was wrapped in an anonomous function.

(function(){   ... })(); 

Is this something which helps not to pollute the global namespace? Why is it there and how does it work?

Answer 1

It uses the function body to provide its own scope rather than introducing a large number of globals that could be accidentally changed by external code.

Eg.

(function (){     var someConstantValue = ...;     myCoolFunction = function(){ return someConstantValue * 5; } })();  myCoolFunction(); 

If the function scope were not introduced it would be possible to accidentally change someConstantValue by introducing other code (or another library)

someConstantValue = someOtherValue; // this won't change the behaviour of myCoolFunction