Episode 10 : Closures in JS

Function bundled along with it's lexical scope is closure.
JavaScript has a lexcial scope environment. If a function needs to access a variable, it first goes to its local memory. When it does not find it there, it goes to the memory of its lexical parent. See Below code, Over here function y along with its lexical scope i.e. (function x) would be called a closure.
```
function x() {
    var a = 7;
    function y() {
        console.log(a);
    }
    return y;
}
var z = x();
console.log(z);  // value of z is entire code of function y.
```
- In above code, When y is returned, not only is the function returned but the entire closure (fun y + its lexical scope) is returned and put inside z. So when z is used somewhere else in program, it still remembers var a inside x()
Another Example

    function z() {
        var b = 900;
        function x() {
            var a=7;
            function y(){
                console.log(a,b);
            }
            y();
        }
        x();
    }
    z();    // 7 900

Thus In simple words, we can say:
- A closure is a function that has access to its outer function scope even after the function has returned. Meaning, A closure can remember and access variables and arguments reference of its outer function even after the function has returned.

Advantages of Closure:
- Module Design Pattern
- Currying
- Memoize
- Data hiding and encapsulation
- setTimeouts etc.
Disadvantages of Closure:
- Over consumption of memory
- Memory Leak
- Freeze browser

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Namaste Javascript

Episode 10 : Closures in JS