Day 164th: Four modes of JS method invocation

four modes of JS method invocation1. Method Invocation Mode

1 functionpersion () {2     varname1 = "Itcast",3Age1 = 19,4Show1 =function() {5Console.log ( This. Name);6     };7 8     return {9 Age:age1,Ten name:name1, One Show:show1 A     }; - } -  the varp =Newpersion (); -  p.show ();  //The this in the Show method points to the P object. 

2. function call mode

1 function Add (A, b) {2     this. result = a + b; 3 }45  Add (3, 9); // when this method executes, this points to the window 6 7 Console.log (result);   

3. constructor Invocation mode

1 functionpersion () {2      This. Name = "123";3      This. Age = 19;4      This. Show =function(){5Console.log ( This. Name);6     };7 }8 9 varp =Newpersion ();Ten p.show ();//in the Show method, method this, which points to the P object instance. 

4.call and apply mode

1 functionAdd (A, b) {2      This. result = A +B;s3 }4 5 varp = {};//defines an empty object. 6Add.call (p,3,4);    //when this method is called, this points to the P7 Console.log (p.result);8 9 //apply and call are the same usage, except that the second argument is passed with an array. 

variable Promotion : Before the function executes, all the variables in the function are moved to the first declaration.

function Name Promotion scripts in script , before executing, will first compile all the functions in the script to parse, and then execute the normal js code.

Day 164th: Four modes of JS method invocation