可选链操作符?.和空值合并运算符??

[YutHelloWorld]

可选链操作符
空值合并运算符

const adventurer = {
  name: 'Alice',
  cat: {
    name: 'Dinah'
  }
};

const dogName = adventurer.dog?.name;
console.log(dogName);
// expected output: undefined

console.log(adventurer.someNonExistentMethod?.());
// expected output: undefined

?.等价于

let temp = obj.first;
let nestedProp = ((temp === null || temp === undefined) ? undefined : temp.second);

空值运算符：

const foo = null ?? 'default string';
console.log(foo);
// expected output: "default string"

const baz = 0 ?? 42;
console.log(baz);
// expected output: 0