Answer 1

function test(str) {
  str = str.split('').map(item => {
    if (item === item.toUpperCase()) {
      return item.toLowerCase();
    } else {
      return item.toUpperCase();
    }
  }).join('');
  console.log(str);
}

Answer 2

比如重试 5 次

let time = () => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      reject("error");
    }, 1000);
  });
};

async function f(retry = 5) {
  while (retry !== 0) {
    try {
      const result = await time();
      return result;
    } catch (e) {
      if (--retry === 0) {
        throw e
      }
    }
  }
}

Answer 3

async function test() {
  const tt = await setTimeout(() => {console.log(333)}, 3000)
  console.log(444)
  console.log(tt)
}
test()
// 444
// 562
// Promise{<resolved>: undefined}
// 333

不是promise会转为promise，resolved后就继续往下执行了

async function test() {
  const tt = await Promise.resolve(setTimeout(() => {console.log(333)}, 3000))
  console.log(444)
  console.log(tt)
}
test()