text: /*
   * @Author: Blue
   * @Date: 2019-05-25 17:57:25
   * @Last Modified by: blue
   * @Last Modified time: 2019-05-25 17:57:25
   */
  
  
   //Class
  
   class addNub {
      files = 0;
      add() {
          this.files ++;
      };
   };
  
   class insertFile extends addNub {
       files = 2;
   };
   
   let a = new insertFile();
  
  
  //call
  
  function addNub2() {
      this.files = 0;
      this.add = function() {
          this.files ++;
      }
  };
  
  function insertFile2() {
      this.files = 4;
  };
  
  let a2 = new insertFile2();
  addNub2.call( a2 );
  
  
  //prototype
  
  function addNum3() {
      this.files = 0;
      this.add = function() {
          this.files ++;
      }
  };
  
  function insertFile3(){};
  
  insertFile3.prototype = new addNum3();
  
  let a3 = new insertFile3();
  
  
  //Object.create
  
  function addNum4() {
      this.files = 0;
      this.add = function() {
          this.files ++;
          console.log( this );
      }
  };
  
  let a4 = Object.create(addNum4 );
  
  