如何使用變量作為對象內部的索引？ （Javascript）

Question

我正在嘗試使用變量 appetizer、main 和甜點作為數組的索引，但我不知道如何做到這一點。 這是在第 49 行。

    var menu = {
  _courses: {
    appetizers: [],
    mains: [],
    desserts: []
  },
get appetizers() {
   return this._courses.appetizers;
},
get mains() {
  return this._courses.mains;
},
get desserts() {
  return this._courses.desserts;
},
set appetizers(appetizers) {
    this.courses.desserts = desserts;
  },
set mains(mains) {
   this.mains = mains;
},
set desserts(desserts) {
     this.desserts = desserts;
  },
  get courses() {
    return {
      appetizers,
      mains,
      desserts,
    };
  },
  addDishToCourse (courseName, dishName, dishPrice) { 
   const dish = {
     food: courseName,
     name: dishName,
     price: dishPrice,

   };
  return this._courses[courseName].push(dish);
  },
     getRandomDishFromCourse: function(courseName) {
    var dishes = this._courses[courseName];
     if (dishes !== undefined) {
       var randomIndex = Math.floor(Math.random() * dishes.length);
      return randomIndex;
     }
  },

  generateRandomMeal: function() { //This is the problem.
   var appetizer = this.getRandomDishFromCourse('appetizers');
    var main = this.getRandomDishFromCourse('mains');
    var dessert = this.getRandomDishFromCourse('dessert');
    return 'Your meal is ' + appetizer + ', ' + main + ', and ' + dessert + '. The total price is $' +/* this.dish.price */ 8 + '.'; 
  }
}; 

menu.addDishToCourse('appetizers', 'Bread Loaf', 4.25);
menu.addDishToCourse('appetizers', 'Caesar Salad', 3.50);
menu.addDishToCourse('appetizers', 'Small Soup', 4.50);
menu.addDishToCourse('mains', 'Steak Dinner', 20.00);
menu.addDishToCourse('mains', 'spaghetti', 16.00);
menu.addDishToCourse('mains', 'Turkey Dinner', 18.99);
menu.addDishToCourse('desserts', 'Icecream', 5.99);
menu.addDishToCourse('desserts', 'Cookies', 5.99);
menu.addDishToCourse('desserts', 'Jello', 5.99);


var meal = menu.generateRandomMeal();
console.log(meal);

我曾嘗試使用此代碼：

this.appetizers[appetizer]
this.mains[main]
this.desserts[dessert]

但這只是返回 Object 對象代替索引號。

Answer 1

你的getRandomDishFromCourse從傳遞的courseName選擇一個隨機索引，但它只返回索引 - 它應該通過return dishes[randomIndex];返回一個dish對象return dishes[randomIndex]; .

菜品返回后，在generateRandomMeal ，您需要選擇每個菜品的name屬性進行打印，並將所有price相加得到總價：

  getRandomDishFromCourse: function(courseName) {
    var dishes = this._courses[courseName];
    if (dishes !== undefined) {
      var randomIndex = Math.floor(Math.random() * dishes.length);
      return dishes[randomIndex];
    }
  },

  generateRandomMeal: function() { //This is the problem.
    var appetizer = this.getRandomDishFromCourse('appetizers');
    var main = this.getRandomDishFromCourse('mains');
    var dessert = this.getRandomDishFromCourse('desserts');
    return 'Your meal is ' + appetizer.name + ', ' + main.name + ', and ' + dessert.name +
      '. The total price is $' + (appetizer.price + main.price + dessert.price).toFixed(2)
  }

 var menu = { _courses: { appetizers: [], mains: [], desserts: [] }, get appetizers() { return this._courses.appetizers; }, get mains() { return this._courses.mains; }, get desserts() { return this._courses.desserts; }, set appetizers(appetizers) { this.courses.desserts = desserts; }, set mains(mains) { this.mains = mains; }, set desserts(desserts) { this.desserts = desserts; }, get courses() { return { appetizers, mains, desserts, }; }, addDishToCourse(courseName, dishName, dishPrice) { const dish = { food: courseName, name: dishName, price: dishPrice, }; return this._courses[courseName].push(dish); }, getRandomDishFromCourse: function(courseName) { var dishes = this._courses[courseName]; if (dishes !== undefined) { var randomIndex = Math.floor(Math.random() * dishes.length); return dishes[randomIndex]; } }, generateRandomMeal: function() { //This is the problem. var appetizer = this.getRandomDishFromCourse('appetizers'); var main = this.getRandomDishFromCourse('mains'); var dessert = this.getRandomDishFromCourse('desserts'); return 'Your meal is ' + appetizer.name + ', ' + main.name + ', and ' + dessert.name + '. The total price is $' + (appetizer.price + main.price + dessert.price).toFixed(2) } }; menu.addDishToCourse('appetizers', 'Bread Loaf', 4.25); menu.addDishToCourse('appetizers', 'Caesar Salad', 3.50); menu.addDishToCourse('appetizers', 'Small Soup', 4.50); menu.addDishToCourse('mains', 'Steak Dinner', 20.00); menu.addDishToCourse('mains', 'spaghetti', 16.00); menu.addDishToCourse('mains', 'Turkey Dinner', 18.99); menu.addDishToCourse('desserts', 'Icecream', 5.99); menu.addDishToCourse('desserts', 'Cookies', 5.99); menu.addDishToCourse('desserts', 'Jello', 5.99); var meal = menu.generateRandomMeal(); console.log(meal);

（ toFixed(2)需要在 total 之后以避免浮點問題）

Answer 2

您需要使用索引來訪問數組中的項目。 你現在擁有它的方式只會打印隨機索引。

 var menu = { _courses: { appetizers: [], mains: [], desserts: [] }, get appetizers() { return this._courses.appetizers; }, get mains() { return this._courses.mains; }, get desserts() { return this._courses.desserts; }, set appetizers(appetizers) { this.courses.desserts = desserts; }, set mains(mains) { this.mains = mains; }, set desserts(desserts) { this.desserts = desserts; }, get courses() { return { appetizers: this.appetizers, mains: this.mains, desserts: this.desserts, }; }, addDishToCourse(courseName, dishName, dishPrice) { const dish = { food: courseName, name: dishName, price: dishPrice, }; return this._courses[courseName].push(dish); }, getRandomDishFromCourse: function(courseName) { var dishes = this._courses[courseName]; if (dishes !== undefined) { var randomIndex = Math.floor(Math.random() * dishes.length); return randomIndex; } }, generateRandomMeal: function() { //This is the problem. var appetizer = this.appetizers[this.getRandomDishFromCourse('appetizers')]; var main = this.mains[this.getRandomDishFromCourse('mains')]; var dessert = this.desserts[this.getRandomDishFromCourse('desserts')]; return 'Your meal is ' + appetizer.name + ', ' + main.name + ', and ' + dessert.name + '. The total price is $' + /* this.dish.price */ 8 + '.'; } }; menu.addDishToCourse('appetizers', 'Bread Loaf', 4.25); menu.addDishToCourse('appetizers', 'Caesar Salad', 3.50); menu.addDishToCourse('appetizers', 'Small Soup', 4.50); menu.addDishToCourse('mains', 'Steak Dinner', 20.00); menu.addDishToCourse('mains', 'spaghetti', 16.00); menu.addDishToCourse('mains', 'Turkey Dinner', 18.99); menu.addDishToCourse('desserts', 'Icecream', 5.99); menu.addDishToCourse('desserts', 'Cookies', 5.99); menu.addDishToCourse('desserts', 'Jello', 5.99); //console.log(JSON.stringify(menu, null, 4)); console.log(menu.generateRandomMeal());