javascript - 一个数组中的对象字面量和对象构造函数是否存在潜在问题？

Question

我想深入了解 JavaScript 中的对象创建。一般来说，我了解创建方法之间的差异等。当我使用下面两种方式创建数组中的对象时，您能描述一下这两种情况下使用对象数组的区别和影响吗？

function Animal(name, species) {
  this.name = name,
  this.species = species
}

var animals = [
  {name: 'azor', species: 'dog'},
  {name: 'mruczek', species: 'cat'},
  {name: 'burek', species: 'dog'},
];

//Case 1
newAnimal = {name: 'motek', species: 'buterfly'}
animals.push(newAnimal);
console.log(animals);

console.log('---');

//Case 2
newAnimal = new Animal('bongo', 'elephant');
animals.push(newAnimal);
console.log(animals);

我问是因为如果我使用控制台它会显示

[ { name: 'azor', species: 'dog' },
  { name: 'mruczek', species: 'cat' },
  { name: 'burek', species: 'dog' },
  { name: 'motek', species: 'buterfly' } ]
---
[ { name: 'azor', species: 'dog' },
  { name: 'mruczek', species: 'cat' },
  { name: 'burek', species: 'dog' },
  { name: 'motek', species: 'buterfly' },
  Animal { name: 'bongo', species: 'elephant' } ]

问题

像//Case 2一样，在同一个数组中使用文字和构造函数创建对象是否有问题？

Answer 1

如果您希望所有对象都真正成为 Animal 实例，您可以使用 Object.setPrototypeOf()重新定义对象的原型(prototype):

class Animal {
  constructor (name, species) {
    this.name = name;
    this.species = species;
  }

  greet () {
    return `My name is ${this.name} and I am a ${this.species}`;
  }
}

var animals = [
  {name: 'azor', species: 'dog'},
  {name: 'mruczek', species: 'cat'},
  {name: 'burek', species: 'dog'},
];

animals.push({name: 'motek', species: 'buterfly'});
animals.push(new Animal('bongo', 'elephant'));

animals.forEach(animal => {
  Object.setPrototypeOf(animal, Animal.prototype)
});

console.log(`Are all the animals actually an Animal? ${
  animals.every(animal => animal instanceof Animal)
}`);
console.log(animals.map(animal => animal.greet()));

或者您可以使用多态性形式将所有对象视为动物，方法是使用 Function.prototype.call() :

class Animal {
  constructor (name, species) {
    this.name = name;
    this.species = species;
  }

  greet () {
    return `My name is ${this.name} and I am a ${this.species}`;
  }
}

var animals = [
  {name: 'azor', species: 'dog'},
  {name: 'mruczek', species: 'cat'},
  {name: 'burek', species: 'dog'},
];

animals.push({name: 'motek', species: 'buterfly'});
animals.push(new Animal('bongo', 'elephant'));

// animals.forEach(animal => {
//   Object.setPrototypeOf(animal, Animal.prototype)
// });

console.log(`Are all the animals actually an Animal? ${
  animals.every(animal => animal instanceof Animal)
}`);
console.log(animals.map(animal => Animal.prototype.greet.call(animal)));

请注意，在这种情况下，它们仍然是最初定义的，但您可以调用 Animal 的 prototype 方法，并将每个实例作为调用上下文传递。

哦，console.log() 输出不同的原因是 [Symbol.toStringTag]属性，您可以重载:

var newAnimal = {name: 'motek', species: 'buterfly', [Symbol.toStringTag]: 'Animal'}
console.log(newAnimal);
// Animal {name: "motek", species: "buterfly", Symbol(Symbol.toStringTag): "Animal"}