Four ways to invoke the JS type function

function CallThis point: Window return value: Determined by the return value, if there is no return statement, it means that there is no value returned

Case 1:function F1 () {    console.log (this);} F1 ();       Window case 2:function F2 () {    return function () {        console.log (this);}    } var f2n = F2 (); f2n ();               This-->window  This is also a function call pattern Case 3:functioon F3 () {    f3n ();        The calling mode of the function--->window function    f3n () {        console.log (this);}    } F3 ();

　　

Method InvocationThis point: The caller return value of the method: determined by the return statement

   Code Listing 1:    var obj={        age:10,        say:function () {            console.log (this.age);        }    };    Obj.say ();//method call pattern    Code 2:    function F1 () {        console.log (this);    }    var obj2={        s1:f1//Assigns the value of the F1 function to the OBJ2.S1 attribute    };    OBJ2.S1 ();//method call pattern-->this:obj2    Code 3:    var obj3={        age:10,        s1:function () {            Console.log ( this.age);        }    };    var obj4={        age:20,        s2:obj3.s1//assigns the value of the OBJ3.S1 function to the S2 property    };    OBJ4.S2 ();//method invocation mode: This-->obj4    function f5 () {    }    var a1=f5 ();//undefeind    var a2=f5;// A2 is a function

　　

Constructor Call        This point: Object created by the current constructor         return value  :   A, no manually added return value, default return this  &N Bsp                         B, return a basic data type (number, Boolean, NULL, undefine D), final return this                            C, return a complex The data type (object) that eventually returns the object

    Code Listing 1:    function person () {        this.age =;        THIS.name = "Zhang San";        Console.log (this);    }    Constructor call pattern:    var p1 = new Person ();//Print out the instance person {age:20, name: "Zhang San"}    code 2;    function P2 () {        this.age = ;        Return "ABC";    }    var P2 = new P2 ();    Console.log (p2); P2 {age:18}    code 3:    function P3 () {        this.age = ten;        return {};    }    var p3 = new P3 ();    Console.log (p3); Object {}    Console.log (p3.age);//undefined    Code 4:    function P4 () {        this.age = ten;        return [1, 3, 5];    }    var P4 = new P4 ();    Console.log (p4);//[1, 3, 5]    console.log (p4.age);//undefined

　　

Context callsCall and apply are methods, which are methods that all functions have. Function.prototype
as long as the function calls the Call/apply method, the function executes immediately.
This points to: A, pass a null/undefined------------------->window B, pass a number, string, Boolean-------> corresponding basic wrapper class Type Object C, pass an object-------------------------------> point to the return value of the object: determined by the return statement

    Function F1 () {        console.log (this);    }    Context mode    f1.call (null);          Window    f1.call (undefined);     Window    F1.call (1);             Instance of number    F1.call ("abc");         Instance of string    F1.call (true);          The Boolean instance    var s1= "abc";           The code internally creates an instance of the string constructor that corresponds to the strings                            //        {0: "A", 1: "B", 2: "C", length:3}                            //After the execution of the code, the instance is destroyed    Console.log (s1.length); 3    Console.log (s1[0]);     A

　　

Four ways to invoke the JS type function