如何在其他构造函数中调用构造函数？

function Person(name, age) {
  this.name = name;
  this.age = age;
}

function Student(name, age, grade) {
  Person.call(this, name, age);
  this.grade = grade;
}

var student = new Student("John", 18, "A");
console.log(student.name);  // 输出 "John"
console.log(student.age);   // 输出 18
console.log(student.grade); // 输出 "A"

function Person(name, age) {
  this.name = name;
  this.age = age;
}

function Student(name, age, grade) {
  Person.apply(this, [name, age]);
  this.grade = grade;
}

var student = new Student("John", 18, "A");
console.log(student.name);  // 输出 "John"
console.log(student.age);   // 输出 18
console.log(student.grade); // 输出 "A"

function Person(name, age) {
  this.name = name;
  this.age = age;
}

function Student(name, age, grade) {
  var student = Object.create(Person.prototype);
  student.name = name;
  student.age = age;
  student.grade = grade;
  return student;
}

var student = new Student("John", 18, "A");
console.log(student.name);  // 输出 "John"
console.log(student.age);   // 输出 18
console.log(student.grade); // 输出 "A"