Closure

A closure is a combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment).

In other words, a closure gives you access to an outer function’s scope from an inner function. In JavaScript, closures are created every time a function is created, at function creation time.

function add(num: number) {
  return function(num2: number) {
    return num + num2;
  }
}

console.log(add(5)(5));

Closure: Define what variables are accessible inner functions or blocks of code.

function createTaxCalculator(tax) {
    function calculateTax(amount) {
        return amount * tax;
    }
    return calculateTax;
}

const calculateVatAmount = createTaxCalculator(0.19);
const calculateIncomeTaxAmount = createTaxCalculator(0.25);

console.log(calculateVatAmount(100));
console.log(calculateVatAmount(200));