using async await and .then together

问题:

Is there any harm in using async/await and .then().catch() together such as:

async apiCall(params) {
    var results = await this.anotherCall()
      .then(results => {
        //do any results transformations
        return results;
      })
      .catch(error => {
        //handle any errors here
      });
    return results;
  }

回答1:

An async function can contain an await expression that pauses the execution of the async function and waits for the passed Promise's resolution, and then resumes the async function's execution and returns the resolved value.

As you can see from below example that you can use two ways to handle await result and errors,The keyword await makes JavaScript wait until that promise settles and returns its result (One you get from resolved promise).So as such there is no harm (I don't fully understand what you refer as harm here).

function returnpromise(val) {
  return new Promise((resolve, reject) => {
    if (val > 5) {
      resolve("resolved"); // fulfilled
    } else {
      reject("rejected"); // rejected
    }
  });
}

//This is how you handle errors in await
async function apicall() {
  try {
    console.log(await returnpromise(5))
  } catch (error) {
    console.log(error)
  }
}

async function apicall2() {
  let data = await returnpromise(2).catch((error) => {
    console.log(error)
  })
}

apicall2();
apicall();

For further reference have a look at-MDN DOCS

回答2:

I always use async/await and .catch() instead of using async/await and try/catch to make code compactly.

async function main() {
  const result = await asyncTask().catch(error => console.error(error));
}

回答3:

If you use Async/await you don't need to chain .then() just store the result returned by you resolve() in a variable (response in the example) but if you want to handle the errors you have to try/catch your code :

async function f() {

  try {
    let response = await fetch('http://no-such-url');
  } catch(err) {
    alert(err); // TypeError: failed to fetch
  }
}

in your promise use:

throw new Error("oops!");

Or

Promise.reject(new Error("Whoops!"));