1// closure in javascript
2-> A closure gives you access to an outer function’s scope
3   from an inner function
4
5const outerFun = (a) => {
6  let b = 10;
7  // inner func can use variable/parameter of outer funcion
8  const innerFun = () => {
9    let sum = a + b; 
10    console.log(sum);
11  }
12  return innerFun;
13}
14let inner = outerFun(5);
15inner();

1function outer() {
2  var counter = 0; // Backpack or Closure
3  function incrementCounter() {
4    return counter++;
5  }
6  return incrementCounter;
7}
8
9const count = outer();
10count(); // 0
11count(); // 1
12count(); // 2

1function makeFunc() {
2  var name = 'Mozilla';
3  function displayName() {
4    alert(name);
5  }
6  return displayName;
7}
8
9var myFunc = makeFunc();
10myFunc();
11

1var counter = (function() {
2  var privateCounter = 0;
3  function changeBy(val) {
4    privateCounter += val;
5  }
6  return {
7    increment: function() {
8      changeBy(1);
9    },
10    decrement: function() {
11      changeBy(-1);
12    },
13    value: function() {
14      return privateCounter;
15    }
16  };
17})();
18
19console.log(counter.value()); // logs 0
20counter.increment();
21counter.increment();
22console.log(counter.value()); // logs 2
23counter.decrement();
24console.log(counter.value()); // logs 1
25