what is a closure in javascript

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();

1A closure gives you access to an outer function’s scope from an inner function
2//example
3function init() {
4  var name = 'Mozilla'; // name is a local variable created by init
5  function displayName() { // displayName() is the inner function, a closure
6    alert(name); // use variable declared in the parent function
7  }
8  displayName();
9}
10init();
11

1function makeAdder(x) {
2  return function(y) {
3    return x + y;
4  };
5}
6
7var add5 = makeAdder(5);
8var add10 = makeAdder(10);
9
10console.log(add5(2));  // 7
11console.log(add10(2)); // 12

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 OuterFunction() {
2
3    var outerVariable = 100;
4
5    function InnerFunction() {
6        alert(outerVariable);
7    }
8
9    return InnerFunction;
10}
11var innerFunc = OuterFunction();

1//Closures are the inner functions that are embedded in parent function
2function getName(){
3    // print name function is the closure since it is child function of getName
4     function printName(){
5         return 'Kevin'
6     }
7     // return our function definition
8     return printName;
9}
10
11const checkNames = getName();
12console.log(checkNames());