一般繼承是出現的問題

    function people(name,sex){
      this.name=name;
      this.sex=sex;
    }
    people.prototype.showname=function(){
      alert(this.name);
    }
    function student(name,sex,job){
      people.call(this,name,sex);
      this.job=job;
    }
    student.prototype = people.prototype;//
 
對象賦給對象，就會出現對象的引用，如果子類原型添加一個方法，父類就會受影響
    var p1=new people(‘jack‘,32);
    var s1=new student(‘jenny‘,24,‘student‘);
    console.log(p1);
    console.log(s1);

拷貝繼承

  function people(name,sex){
      this.name=name;
      this.sex=sex;
    }
    people.prototype.showname=function(){
      alert(
 
this.name);
    }
    function student(name,sex,job){
      people.call(this,name,sex);//屬性繼承：調用父類的構造函數
      this.job=job;
    }

    extend(student.prototype,people.prototype);//拷貝繼承,利用for in 實現方法的繼承
    student.prototype.showjob=function(){
      alert();
    }
    function extend(obj1,obj2){
      
 
for (var attr in obj2) {
        obj1[attr]=obj2[attr];
      }
    }
    var p1=new people(‘jack‘,32);
    var s1=new student(‘jenny‘,24,‘student‘);

    console.log(p1);
    console.log(s1);

js對象繼承