SOURCE

// Person类
function Person (name) {
    let age;
    this.name = name;
    this.setAge = function (num) {
        age = num;
    }
    this.getAge = function () {
        return age;
    }
}

// 继承Person的Teacher类
function Teacher () {
    let studentCount;
    this.setStudentCount = function (num) {
        studentCount = num;
    }
    this.getStudentCount = function () {
        return studentCount;
    }
}
Teacher.prototype = new Person ();
Teacher.prototype.constructor = Teacher;