javascript .push 未定义

Question

我正在使用代码训练营并且遇到了语法错误，我只是遇到了很多麻烦，我愿意打赌这非常简单。

// this guy here

return this._courses[courseName].push(dish);

//on this page

const 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.appetizers = appetizers;
  },
  set mains(mains) {
    this._courses.mains = mains;
  },
  set desserts(desserts) {
    this._courses_desserts = desserts;
  },

  get courses() {
    return {
      appetizers: this.appetizers,
      mains: this.mains,
      desserts: this.desserts
    };
  },
  addDishToCourse(courseName, dishName, dishPrice) {
    const dish = {
      name: dishName,
      price: dishPrice,
    };

    return this._courses[courseName].push(dish);                      //this is where its located

  },
  getRandomDishFromCourse(courseName) {
    const dishes = this._courses[courseName];
    const randomIndex = Math.floor(Math.random() * dishes.length);
    return dishes[randomIndex];
  },

  generateRandmMeal() {
    const appetizer = getRandomDishFromCourse('appetizer');
    const main = getRandomDishFromCourse('main');
    const dessert = getRandomDishFromCourse('dessert');
    const totalPrice = appetizer.price + main.price + dessert.price;
    return `your meal is ${appetizer.name}, ${main.name}, ${dessert.name} and your total is ${totalPrice}`;
  }
};

menu.addDishToCourse('appetizer', 'wings', 4.00);
menu.addDishToCourse('main', 'bruh', 5.00);
menu.addDishToCourse('dessert', 'dude', 3.00);

对于我的生活，我无法弄清楚为什么语法 .push 说的是未定义。我一遍又一遍地看视频，我就是没有进步，我可以从头开始，但我想先了解为什么会这样.谢谢你

Answer 1

_courses: {
      appetizers:[],
      mains:[],
      desserts:[]
    },

开胃菜 - menu.addDishToCourse('appetizers','wings',4.00);

mains - menu.addDishToCourse('mains','bruh',5.00);