Closures in JavaScript

 Closure is a function along with its lexical environment forms a closure that is called closure.

What is lexical Environment?

    In Simple language lexical scope  is a variable defined outside your scope or upper scope is automatically available inside your scope which means you don't need to pass it here.

let str = "javaScript";
 myFun = () => {
    console.log(str);
}
myFun();

What happen line 4. so inside c() it forms a closure with the a() lexical scope. c() function is bind to the variable of b that means if forms a closure and it has access to parent lexical scope.

function x() {
    var a = 10;
    function y() {
        console.log(a);
    }
    return y;
}
var z = x();
console.log(z);
z();

consider this example x() it return function y so what will print in console, yeah it print function y like

function y(){
    console.log(a);
}

and what will be return after calling z()?

it return 7 but why?

because this is not return only y function, it return whole closure. the closure enclosed function along with its lexical environment that was return and it was put inside z so that's why it return 7.  

function along with its lexical bundle together form a closure.

for this example, function along with its scope that's is closure.