Summarize _javascript skills of several common writing methods of JS object-oriented

Define circle class, owning member variable r, constant pi, and member function area ()

1. Factory mode

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 wording

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 wording

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

4. It's a bit of a change, but the essence is 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 put into the attribute to write this. pi=3.14159;

Commonly used as the first and third

Extended small instance of the third way of writing

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 ();

Note that this is the point of issue

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