js技巧

if...else...

function getAge(age) {
  if (age <= 12) {
    return "儿童";
  } else if (age > 12 && age <= 28) {
    return "青年";
  } else if (age > 28 && age <= 50) {
    return "青年";
  } else {
    return "老年";
  }
}
console.log(getAge(54));

const foodMap = {
  香蕉: 20,
  苹果: 12,
  草莓: 33,
  菠萝: 21,
};
function getFood(name) {
  return foodMap[name];
}
console.log(getFood("草莓"));

const foods = [
  {
    name: "香蕉",
    price: 12,
  },
  {
    name: "苹果",
    price: 13,
  },
  {
    name: "菠萝",
    price: 14,
  },
  {
    name: "葡萄",
    price: 14,
  },
  {
    name: "蜜枣",
    price: 15,
  },
];
// 找出价格为14的水果
const name = foods.filter((i) => i.price === 14).map((k) => k.name);
console.log(name); // ['菠萝', '葡萄']
const apple = foods.find((i) => i.name === "苹果" && i.price === 13);
console.log("apple", apple); // {name: '苹果', price: 13}

运算符

if (val !== null && val !== undefined) {
  const num = val;
} else {
  const num = "";
}
const num = val ?? "";