Javascript is one of the many languages that support ‘closure’ scopes.

Let us take a normal piece of JS code -

function myFun () {
    var myVar = "some value";


console.log(myVar); //undefined

When we run it, ovbiously, we would get an error on the last line because myVar is not present in the scope anymore, as we are outside the function.

Now consider this piece of code

function funcGen () {
    var someVal = 10;
    function aFun () {
        return someVal

    return aFun

var myFun = funcGen();

console.log(myFun()); //11
console.log(myFun()); //12

In this example, we are creating a new function inside funcGen and returning it. When we do that. The returned value is a function myFun which itself can be called like we have done in the last line.

When we do that, we will see that 11 and 12 are printed (doing ++ on 10 twice) When we are on the last two lines, funcGen scope has ended, and hence we should not be able to access someVal, but we are able to, because of closure.

The function aFun, since it is created inside funcGen gets access to all local variables of funcGen and continues to have access to them after the scope of funcGen has ended. This scope that a function inherits from the parent function is called a closure scope.