Async/Await vs new Promise(resolve,reject)

Question

Is there any differences between async/await, and more standard promise notations using .then , .finally , and .catch

for example

functionThatReturnsPromise(someVar).then((returnedValueFromPromise) => {
    console.log(returnedValueFromPromise)
})

vs

async functionThatReturnsPromise(someVar)  {
    await returnedValueFromPromise
}

I'm unsure if Promise chaining is just the old notation, and it's been replaced by the newer async/await. Is there still a use case for both? What is better practice?

Answer 1

It all depends on what you want. async / await are new. Think of it this way, they allow a promise to run like it was synchronous when it isn't.

Moreover using async / await makes your code cleaner and more readable. And to answer your question, there are not much differences between them in terms of what they do. The syntax is just quite different.

Promise chaining is not old fashion, they are quite new, just that async / await came a bit later - giving you a "better" way of handling Promises.

Finally, you can use them interchangeably in your code.

Answer 2

You're misunderstanding how it works. With async/await you have a synchronous syntax flow of the code execution that's it:

try {
  const returnedValueFromPromise = await functionThatReturnsPromise(someVar);
} catch (err) {
  console.error(err);
  throw err
}

Notice that

• Code block must be inside an async scoped function
• You still need to do err handling, can't assume promise will always work good
• All values returned by async enclosed function are promises by default

Answer 3

使用await需要注意的是，您需要将await语句包装在try catch block中，以防请求失败，我个人认为这比常规的 promise 链接更丑陋。