主页 / 问题 / 841032
Accepted
Semerkin
Asked:2020-06-12 19:30:59 +0800 CST2020-06-12 19:30:59 +0800 CST

调用原型方法时出错

  • 772

有这个代码：

'use strict'
var collectionProto = {
  values: function() {
    return this;
  },
  count: function() {
    return this.length;
  },
  at: function(index) {
    return (index > this.length) ? this[index - 1] : null;
  },
  append: function(value) {
    (isArray(value)) ? this.concat(value): this.push(value);
  },
  removeAt: function(index) {
    if (index > this.length) {
      return false;
    }
    this.splice(index - 1, 1);
    return true;
  }
};

function Collection() {
  //this = [];
  return [];
}
Collection.prototype = collectionProto;
Collection.prototype.constructor = Collection;

var numbers = new Collection();
console.log(numbers.values());

其实错误

TypeError: numbers.values 不是函数

还有两个问题：

  1. 为什么会弹出错误？
  2. 为什么不能在构造函数中写this = []？毕竟this，这里是创建默认解释器的对象。
javascript

3 个回答

  1. Best Answer
    1. 您正在返回一个数组，而不是构造函数创建的对象。
    2. this是一个服务构造，它不能被覆盖。是的，有什么意义？

    'use strict'
var collectionProto = {
    answer: 42
};

function Collection() {
  this.question = 'The Ultimate Question of Life, the Universe, and Everything';
}
Collection.prototype = collectionProto;
Collection.prototype.constructor = Collection;

var numbers = new Collection();
console.log(numbers.question, numbers.answer);

    • 1

  2. 当您从构造函数返回一个对象时，创建的对象会被遗忘。因此（在没有 ES6 的情况下）您可以替换__proto__（在 IE11+ 中支持）：

    'use strict'

var collectionProto = Object.assign(Object.create(Array.prototype), {
  values: function() {
    return this;
  },
  count: function() {
    return this.length;
  },
  at: function(index) {
    return (index > this.length) ? this[index - 1] : null;
  },
  append: function(value) {
    (isArray(value)) ? this.concat(value): this.push(value);
  },
  removeAt: function(index) {
    if (index > this.length) {
      return false;
    }
    this.splice(index - 1, 1);
    return true;
  }
});

function Collection() {
  var me = [];
  me.__proto__ = this.__proto__;
  return me;
}

Collection.prototype = collectionProto;
Collection.prototype.constructor = Collection;

var numbers = new Collection();
console.log(numbers.values());

    • 0 

  3. 'use strict'
var collectionProto = {
  values: [],
  count: function() {
    return this.values.length;
  },
  at: function(index) {
    return (index > this.values.length) ? this.values[index - 1] : null;
  },
  append: function(value) {
    Array.isArray(value) ? this.values.concat(value): this.values.push(value);
  },
  removeAt: function(index) {
    if (index > this.values.length) {
      return false;
    }
    this.values.splice(index - 1, 1);
    return true;
  }
};

function Collection() {}
Collection.prototype = collectionProto;
Collection.prototype.constructor = Collection;

var numbers = new Collection();
console.log(numbers.values);

numbers.append(6757);
console.log(numbers.values);

    • -1

相关问题