Closure:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Closures

• A closure is a function with access to the parent scope, even after the parent function has closed. They help us mimic the behavior of access modifiers through scoping. Let’s show this via an example:

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• 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.

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• In other words, 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.

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Variant #1

// we  used an immediately invoked function expression
// to create a private variable, counter
var counterIncrementer = (function() {
var counter = 0;

    return function() {
        return ++counter;
    };
})();

// prints out 1
console.log(counterIncrementer());
// prints out 2
console.log(counterIncrementer());
// prints out 3
console.log(counterIncrementer());

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Variant #2

function sum(a) {
  return function (b) {
    return b + a;
  };
}

console.log(sum(2)(5)); 
// -> sum(2)(5) should return 7

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function makeAdder(x) {
  return function(y) {
    return x + y;
  };
}

var add5 = makeAdder(5);
var add10 = makeAdder(10);

console.log(add5(2));  // 7
console.log(add10(2)); // 12

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Variant #3

function init() {
  var name = 'Mozilla'; // name is a local variable created by init
  function displayName() { // displayName() is the inner function, a closure
    alert(name); // use variable declared in the parent function
  }
  displayName();
}
init();

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