main.js

// A closure is the 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 makeAdder(x) {
    return function (y) {
      return x + y;
    };
  }
  
  const add5 = makeAdder(5);
  const add10 = makeAdder(10);
  
  console.log(add5(2)); // 7
  console.log(add10(2)); // 12
    
//   In this example, we have defined a function makeAdder(x), that takes a single argument x, and returns a new function. The function it returns takes a single argument y, and returns the sum of x and y.
// In essence, makeAdder is a function factory. It creates functions that can add a specific value to their argument. In the above example, the function factory creates two new functions—one that adds five to its argument, and one that adds 10.
// add5 and add10 are both closures. They share the same function body definition, but store different lexical environments. In add5's lexical environment, x is 5, while in the lexical environment for add10, x is 10.