JavaScript Closures

 

What is a closure?
A closure is an inner function that has access to the outer (enclosing) function’s variables—scope chain. The closure has three scope chains: it has access to its own scope (variables defined between its curly brackets), it has access to the outer function’s variables, and it has access to the global variables.

The inner function has access not only to the outer function’s variables, but also to the outer function’s parameters. Note that the inner function cannot call the outer function’s arguments object, however, even though it can call the outer function’s parameters directly.

Source:

http://javascriptissexy.com/understand-javascript-closures-with-ease/

Example:

function showName (firstName, lastName) {

	​var nameIntro = "Your name is ";
	    // this inner function has access to the outer function's variables, including the parameter​
	​function makeFullName () {
        
	​return nameIntro + firstName + " " + lastName;
    
	}
	​
	​return makeFullName ();

	}

	​
	showName ("Michael", "Jackson"); // Your name is Michael Jackson