What are Closures in Javascript?

Closures are nothing but a statefull functions.

A closure is an inner function that has access to outer function’s variables in addition to it’s own variable and global variables.In simple term a closure is a function inside a function.Closures using Lexical scoping in which function have access to global and outer variables.Below is a sample example of Javascript closure.

function employee() {
    var employee_dept = 'IT';
   
    return {
        getDept: function ()  {           
          return employee_dept;
        },
        setDept: function (new_dept)  {
            employee_dept = new_name;
        }
    }
​
}

var emp1 = employee (); // In this juncture, the employee_dept outer function has returned.​
mjID.getDept(); // IT
mjID.setDept('Account'); // Changes the outer function's variable​
mjID.getDept(); //outputs Account

Closures prevents your important variable to be modified accidently.It can be only modified by itself.