javascript - 您可以在不更改对象构造函数的情况下向对象构造函数添加新的动态参数吗？

Question

我是 Javascript 新手，正在学习对象。我了解到您可以使用原型向对象添加新属性或方法。

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
}

Person.prototype.nationality = "English";

现在我想知道是否也可以在不直接分配新属性或更改对象构造函数的情况下添加带有新参数的新属性。所以，它变成：

function Person(first, last, age, eyecolor, nationality) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
  this.nationality = nationality;
}

标签： javascriptobjectconstructorprototype

Answer 1

您可以通过将原始构造函数包装在新函数中来做到这一点，如下所示：

const originalPerson = Person;
Person = function(first, last, age, eyecolor, nationality) {
    const instance = new originalPerson(first, last, age, eyecolor);
    instance.nationality = nationality;
    return instance;
};

现场示例：

function Person(first, last, age, eyecolor) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eyecolor;
}

const originalPerson = Person;
Person = function(first, last, age, eyecolor, nationality) {
    const instance = new originalPerson(first, last, age, eyecolor);
    instance.nationality = nationality;
    return instance;
};

const joe = new Person("Joe", "Bloggs", 42, "brown", "English");
console.log(joe.nationality);

你也可以通过继承来做到这一点：

const originalPerson = Person;
Person = class extends originalPerson {
    constructor(first, last, age, eyecolor, nationality) {
        super(first, last, age, eyecolor);
        this.nationality = nationality;
    }
};

现场示例：

function Person(first, last, age, eyecolor) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eyecolor;
}

const originalPerson = Person;
Person = class extends originalPerson {
    constructor(first, last, age, eyecolor, nationality) {
        super(first, last, age, eyecolor);
        this.nationality = nationality;
    }
};
const joe = new Person("Joe", "Bloggs", 42, "brown", "English");
console.log(joe.nationality);

在这两种情况下我都重新分配了Person，但你不必这样做，你可以使用ExtendedPerson或类似的：

class ExtendedPerson extends Person {
    constructor(first, last, age, eyecolor, nationality) {
        super(first, last, age, eyecolor);
        this.nationality = nationality;
    }
}

...然后使用new ExtendedPerson(/*...*/).

现场示例：

function Person(first, last, age, eyecolor) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eyecolor;
}

class ExtendedPerson extends Person {
    constructor(first, last, age, eyecolor, nationality) {
        super(first, last, age, eyecolor);
        this.nationality = nationality;
    }
}
const joe = new ExtendedPerson("Joe", "Bloggs", 42, "brown", "English");
console.log(joe.nationality);