Closures.md

Closures.md

To know more bout execution context and lexical environment read here

Used in higher order functions read here

Example 1

var counter = (function() {
    var count = 0;
    function increment() {
        count += 1;
    }
    return {
        increment: function() {
            increment(1);
        },
        getValue: function() {
            return count;
        }
    }
})();

Example 2

function multiplier(num){
	return function (multiplier){
		return num * multiplier
	}
}

var double = multiplier(2)
var triple = multiplier(3)

double(3) // 6
triple(3) // 9

Example 3

//module

function Student(_name,_marks) {
  var username = _name;
  var marks = _marks;

  function get_user() {
    console.log(username);
  }

  function calculate_marks() {
    console.log(marks.reduce((all, item) => (all += item)));
  }

  return {
    get_user: get_user,
    calculate_marks: calculate_marks
  };
}

var s1 = Student('s1',[10,20,30]);

s1.get_user(); // s1
s1.calculate_marks(); // 60

Memoization