What does closure exactly mean in Javascript?

Question

I don't want bookish explanation.

Answer 1

In few words, a closure is a private variable space, not accessible from outside of it...

In JS, mostly closure are created when you open curly brackets to enclose instruction for a function definition:

var A = 42; // defined in the global scope, wich can be considered as root closure

function test() { // creating function create a private context (the closure)
var B = "forty-two"; // defined in the function scope (the function private closure)
console.log(A); // output '42', because global scope always accessible (always in the parent closures tree)
console.log(B); // output 'forty-two', because we are in the scope of B
}

console.log(A); // output '42' (we are in the global scope / same closure)
console.log(B); // 'undefined', because the test() function scope isn't accessible from outside

Answer 2

O I never knew something like that even existed