写好JavaScript条件语句的5条守则

照抄https://juejin.im/post/5bdef288e51d450d810a89c6
 testEquals(fruit) {
      if (fruit === 'apple' || fruit === 'strawberry') {
        console.log('==');
      }
    },
    testIncludes(fruit) {
      const redFruits = ['apple', 'strawberry', 'cherry', 'cranberries'];
      if (redFruits.includes(fruit)) {
        console.log('red');
      }
    },
    testMoreIf(fruit, quantity) {
      const redFruits = ['apple', 'strawberry', 'cherry', 'cranberries'];
      // 条件 1: fruit 必须有值
      if (fruit) {
        // 条件 2: 必须是red的
        if (redFruits.includes(fruit)) {
          console.log('red');
          // 条件 3: quantity大于10
          if (quantity > 10) {
            console.log('big quantity');
          }
        }
      } else {
        console.log('error');
      }
    },
    testMoreNoElse(fruit, quantity) {
      const redFruits = ['apple', 'strawberry', 'cherry', 'cranberries'];
      if (!fruit) console.log('error');
      if (!redFruits.includes(fruit)) return;
      console.log('red');
      if (quantity > 10) console.log('big quantity');
    },
    testOrValue(fruit, quantity) {
      if (!fruit) return;
      // 如果 quantity 参数没有传入，设置默认值为 1
      const q = quantity || 1;
      console.log(`We have ${q} ${fruit}!`);
    },
    testDefaultValue(fruit, quantity = 1) {
      // 如果 quantity 参数没有传入，设置默认值为 1
      if (!fruit) return;
      console.log(`We have ${quantity} ${fruit}!`);
    },
    testSwitch(color) {
      // 使用条件语句来寻找对应颜色的水果
      switch (color) {
        case 'red':
          return ['apple', 'strawberry'];
        case 'yellow':
          return ['banana', 'pineapple'];
        case 'purple':
          return ['grape', 'plum'];
        default:
          return [];
      }
    },
    testInsteadOfSwitch(color) {
      const fruitColor = {
        red: ['apple', 'strawberry'],
        yellow: ['banana', 'pineapple'],
        purple: ['grape', 'plum']
      };
      return fruitColor[color] || [];
    },

 //1.
      this.testEquals('apple'); //==
      this.testIncludes('apple'); //redz
      //2.
      this.testMoreIf(null); // error: No fruits
      this.testMoreIf('apple'); // print: red
      this.testMoreIf('apple', 20); // print: red, big quantity
      this.testMoreNoElse(null); // error: No fruits
      this.testMoreNoElse('apple'); // print: red
      this.testMoreNoElse('apple', 20); // print: red, big quantity
      //3.
      this.testOrValue('banana'); // We have 1 banana!
      this.testOrValue('apple', 2); // We have 2 apple!
      this.testDefaultValue('banana'); // We have 1 banana!
      this.testDefaultValue('apple', 2); // We have 2 apple!
      //4.
      testSwitch(null); // []
      testSwitch('yellow'); // ['banana', 'pineapple']
      testInsteadOfSwitch(null); // []
      testInsteadOfSwitch('yellow'); // ['banana', 'pineapple']