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prototype is for read only. write create create own copy


commentsJavascript sourceExecution result in your current browser
two object share the same prototype cal
   function Circle(r) {
      this.radius=r;
   }
   Circle.prototype.cal=function() {return this.radius*this.radius};

   var circle1=new Circle(10);
  document.write("circle1 "+circle1.cal());
   var circle2=new Circle(11);
  document.write("<br/>circle2 "+circle2.cal());

now, the circle1 provide its own cal function
    circle1.cal=function() {return this.radius*this.radius/2};
    //circle1 already has its own copy of cal function
    document.write("circle1 "+circle1.cal());
    
    //circle2 is still using prototype cal function
    document.write("<br/>circle2 "+circle2.cal());

now, modify the prototype cal
      Circle.prototype.cal=function() {return this.radius*this.radius/10};
    document.write("circle1 "+circle1.cal());
    //nothing change for circle2
    document.write("<br/>circle2 "+circle2.cal());