Summary of several common object-oriented code writing methods in JavaScript

1. Factory way

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. More formal writing method

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 writing method

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

4. There is a slight change, but the essence is the same as the first one

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 put into the attribute and written as this.PI=3.14159;

Commonly used as the first and third types

Extended small example of the third writing method

var show={
    btn:$('.p1'),
    init:function(){
      var that=this;
      alert(this);
      this.btn.click(function(){
          that.change();
          alert(this);
        })
      
    },
    change:function(){
      this.btn.css({'background':'green'});

    }
  }
  show.init();

What needs to be noted is the pointing problem of this

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