JavaScript Object-Oriented programming

Before you learn JS object-oriented programming, you first need to know what is object-oriented. Object-oriented languages have the concept of a class that allows you to create objects that have the same properties and methods. But JS does not have a class concept, so the objects in JS are different from those in other languages.

A JS object can be defined as: "A collection without attributes, whose properties can be basic values, objects, and functions." Each object is created based on a reference type.

JS creates objects in the following two ways:

1. Create an Object instance:

var person = new Object ();

2. Use object literal:

var person ={};

3. Factory mode:

  function Createperson (name,age,job) {      var p = new Object ();     P.name=name;     P.age=age;     P.job=job;    return p;    }   var P1=createperson ("Jack", "front-end Engineer");  var p2= ...;

4. Constructor Mode:

function Person (name,age,job) {     this.name=name;     This.age=age;    This.job=job;     This.sayname=function () {alert (this.name);};     }    var p1= new person ("Jack", "front-end Engineer");   var p2= ...;

Here's a pause, because the constructor pattern is important, and here's an explanation: this is actually going through the following 4 steps:

(1) Create an object;

(2) Assign the constructor scope to this object (so this will point to the newly created object)

(3) Execute the code inside to add attributes to the new object;

(4) Return the new object;

The P1 and P2 created above have a constructor attribute that points to person. and P1 and P2 even if the instance of person is also an instance of object, because all objects inherit from object.

BUG: Each method is recreated on the instance, the function in JS is an object, so you can transfer the function to the outside of the constructor:

function Person (name,age,job) {           this.name=name;          This.age=age;          This.job=job;          this.sayname=sayname;    }     Fucntion Sayname () {        alert ("THIS.name");   }      var p1= ...;      var p2= ...;

5. Prototype Mode:

The function we create has a prototype property, which is a pointer to an object.

JavaScript Object-Oriented programming