Summary of JS Object-Oriented Programming

//Define the Circle class with member variable r, constant PI, and member function area() to calculate the area

1.Factory method

var Circle = function() {
 var obj = new Object();
 obj.PI = 3.14159;
 obj.area = function( r ) {
  return this.PI * r * r;
 }
 return obj;
}
var c = new Circle();
alert( c.area( 1.0 ) );

2.Regular syntax

function Circle(r) {
  this.r = r;
}
Circle.PI = 3.14159;
Circle.prototype.area = function() {
 return Circle.PI; * this.r * this.r;
}
var c = new Circle();1.0); 
alert(c.area());

3.JSON syntax

var Circle={}}
 "PI":3.14159,
 "area":function(r){
   return this.PI * r * r;
  }
});
alert( Circle.area(1.0) );

4. A little change, but the essence is the same as the first

var Circle=function(r){
  this.r=r;
}
Circle.PI = 3.14159; 
Circle.prototype={
 area:function(){
  return this.r*this.r*Circle.PI;
 }
}
var obj=new Circle(1.0);
alert(obj.area());

Circle.PI = 3.14159; Can be written into the attribute as this.PI=3.14159;

Commonly used are the first and third

An extended small example of the third writing method

var show={
  btn:$('.div1'),
  init:function(){
   var that=this;
   alert(this);
   this.btn.click(function(){
     that.change();
     alert(this);
    });
  ,
  change:function(){
   this.btn.css({'background':'green'});
  }
 }
 show.init();

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