Closures

February 15, 2022

A closure is a function which contains its own lexical environment.
It gives you access to the outer functions scope from an inner function.
The term lexical refers to the fact that lexical scoping uses the location where a variable is declared within the source code to determine where that variable is available.

function adder(x) {
  return function(y) {
    // the inner function can access the outer functions scope.
    return x+y; 
  }
}

var add5 = adder(5);
add5(5); // returns 10

var add10 = adder(10);
add10(5); // returns 15

add(5) is a closure function and within its lexical environment x is 5.
add(10) is another closure function and operates in the same manner as add(5) but within its lexical environment x is 10.