Javascript 尝试 Catch 与 Catch 链

Question

I recently ran into a Javascript problem catching errors and thus crashing when exception thrown.

• funcReturnPromise().then().catch()

I had to change this to:

try {
  funcReturnPromise().then()
} catch (e) {
  ...
}

Couldn't find a decent explanation for it, any JS wizards available to enlighten a JS peasant?

Answer 1

If funcReturnPromise() can throw synchronously (which functions that return promises should generally never do), then you do have to catch that synchronous exception with try/catch as you discovered when using regular .then() .

This is one place where async functions can hep you. For example, if you declare funcReturnPromise as async , then the synchronous exception it throws will automatically become a rejected promise and the caller won't ever be exposed to a synchronous exception.

Or, if the caller (your code here) uses await, then you can catch both sycnhronous exceptions and rejected promises with the same try/catch .

So, for example, you could do this:

async function myFunc()
    try {
      let result = await funcReturnPromise();
      console.log(result);
    } catch (e) {
        // this catches both a rejected promise AND
        // a synchronously thrown exception
        console.log(e);
    }
}

Answer 2

As per the docs You can handle error like this:

try {
  funcReturnPromise.then(value => {
    console.log(value); // Success!
  }, reason => {
    console.error(reason); // Error!
  });
} catch (e) {
  console.error(e); // Error!
}