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How do JavaScript closures work?
I was playing around with the Google Closure Compiler, putting in random code to see what it would do.
It rewrote one of my functions to look something like this:
(function(msg) { console.log(msg); })("Hello World!");
Where it appears that "Hello World" is the argument passed as msg to the anonymous function preceding it. I was looking at it for a moment, and had thought that I had seen something similar in jQuery plugins that look something like:
(function( $ ) {
...
})(jQuery);
Which now makes more sense to me, in the scope of conflicts with $. But what is the primary reason or purpose for passing arguments into an anonymous function like this? Why wouldn't you simply define the arguments as variables within the function? Is there any performance or flexibility advantage to writing functions like this?
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Anonymous functions, also known as closures , allow the creation of functions which have no specified name. They are most useful as the value of callable parameters, but they have many other uses. Anonymous functions are implemented using the Closure class.
Anonymous functions are often arguments being passed to higher-order functions or used for constructing the result of a higher-order function that needs to return a function. If the function is only used once, or a limited number of times, an anonymous function may be syntactically lighter than using a named function.
The syntax is simple: you can simply declare the anonymous function and make it execute by just calling it using the parenthesis at the end of the function. You can simply pass the parameters inside the immediate execution of the anonymous function as we have seen in the above example.
Passing arguments to function is a very important aspect of C++ programming. Arguments refer to values that can be passed to a function. Furthermore, this passing of arguments takes place for the purpose of being used as input information.
There is one significant difference connected also to scope. The following code:
(function(msg) { console.log(msg); })("Hello World!");
is in some circumstances cleaner in terms of namespace pollution than this:
var msg = "Hello World!";
console.log(msg);
because the second code leaves variable after it is no longer needed, but may interfere with other parts of the code.
This is especially important when you execute the mentioned code outside any other function: in such case msg variable would be available everywhere on the page, as global variable.
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