Js understood that closures of

　　Personal understanding closure: function defined inside a function, a function of outsourcing internal functions can access variables defined.

　　Features closure: Variable resident memory

　　demo implement a similar function call Counter:

        function Fn () {
             var C = 0 ;
             function Inner () { 
                C + =. 1 ; 
                the console.log (C) 
            } 
            return Inner; 
        } 
        var F1 = Fn (); 
        F1 (); // . 1 
        F1 (); / / 2 C is not released, the memory resident

 

       Use Scenario 1: setTimeout reference function to pass parameters (only the first parameter is a reference setTimeout function)

        function laterCall(a){
            return function(){
                console.log("a:",a)
            }
        }
        var fn2 = laterCall(123);
        setTimeout(fn2,1000)

　　Use Scenario 2: Analog private member

    var module1 = (function(){
        var a = 1;
        var addOne = function(){
            a += 1;
            return a
        };
        var subOne = function(){
            a -= 1;
            return a
        };
        return{
            addOne:addOne,
            subOne:subOne
        }
    })();
    
    module1.addOne()
    module1.subOne()

Use Scenario 3: object-oriented

    function User(name){
        this.say = function(){
            console.log("hello "+ name);
        }
    }
    var user = new User("frank");
    user.say();