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更改我的回调,承诺异步等待

async-await promise callback javascript

-2

Sameer · 技术社区 · 7 年前

我的代码:

回调:

const first = () => {
  console.log('first');
};
const second = (callback) => {
   setTimeout(() => {
    console.log('second');
    callback();
  }, 2000);
};
const third = () => {
   console.log('third');
};

first();
second(third);   OUTPUT: 'first', 'second', 'third'

承诺:

const first = () => new Promise((resolve, reject) => {
  resolve('first');
});
const second = () => new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('second');
  }, 2000);
});
const third = () => {
  console.log('third');
};

first()
 .then((firstPromiseValue) => {
   console.log(firstPromiseValue);
   second()
    .then((secondPromiseValue) => {
      console.log(secondPromiseValue);
      third();
    })
 });   OUTPUT: 'first', 'second', 'third'

const first = new Promise((resolve, reject) => {
  resolve('first');
});
const second = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('second');
  }, 2000);
});
const third = new Promise(function(resolve, reject) {
  resolve('third');
});
Promise.all([first, second, third]).then((values) => {
  console.log(values);
}); OUTPUT: ['first', 'second', 'third']

如何使用async await转换上述代码?

对于javascript应用程序,哪一个是好的流控制?

那么使用async.瀑布等方法的异步库呢。。

顺便问一下,我上面的代码是否正确?

2 回复 | 直到 7 年前

Amadan 7 年前

如何使用async await转换上述代码?

async/await 不是承诺的替代品,而是承诺的替代品 then() catch() . 你仍然会使用承诺。那你就拿这个 first , second 和 third “承诺”部分中的定义,然后:

async function firstSecondThird() {
  let firstPromiseValue = await first();
  console.log(firstPromiseValue);
  let secondPromiseValue = await second();
  console.log(secondPromiseValue);
  third(); // not a promise, no need to await
}
firstSecondThird();

对于javascript应用程序,哪一个是好的流控制?

客观上,没有一个更好;但是 异步/等待 是最可读的,回调是最显式的(带有 then 代码位于中间)。

那么使用async.瀑布等方法的异步库呢。。

顺便问一下,我上面的代码是否正确?

-1

Javier García 7 年前

如何使用async await转换上述代码?

使用 async/await 是使用承诺的另一种方式。这是最美好的视觉,因为你不会迷失在 then/catch

const first = async (value) => {
  return new Promise((resolve, reject) => {
    resolve('first ');
  });
};
const second = async (value) => {
  return new Promise((resolve, reject) => {
    resolve(value + 'second ');
  });
};
const third = async (value) => {
  return new Promise((resolve, reject) => {
    resolve(value + 'third');
  });
};


first('').then(second).then(third).then( value => console.log(value) );

const first = async () => {
  return new Promise((resolve, reject) => {
    resolve('first ');
  });
};
const second = async () => {
  return new Promise((resolve, reject) => {
    resolve('second ');
  });
};
const third = () => {
  return 'third';

};

async function main() {
  
  let firstValue = await first();
  
  let secondValue = await second();
  
  let thirdValue = third();
  
  return  firstValue + ' ' + secondValue + ' ' + thirdValue;
}

main()
  .then(console.log)
  .catch(err => { console.log('Error:', err) });

对于javascript应用程序,哪一个是好的流控制?

通常当你需要在函数的中间使用承诺或者多个异步调用函数时。

我不知道有什么库可以使用async/await。很抱歉