While rethrowing an Error of a rejected Promise, I noticed that the stack trace seem to be incomplete.
For example:
// returns a Promise that is later on rejected.
function a() {
return new Promise((resolve, reject)=>{
setTimeout(()=>reject(new Error("a")), 2000);
});
}
async function b() {
await a();
}
async function c() {
await b();
}
// testing
async function test() {
let printError = (error)=>console.log(error.stack);
await a().catch(printError);
await b().catch(printError);
await c().catch(printError);
}
test();
All three function calls in test() print the following:
Error: a
at <anonymous>:4:31
I would have expected something like:
Error: a
at <anonymous>:4:31
at new Promise (<anonymous>)
at a (<anonymous>:3:12)
at b2 (<anonymous>:13:15)
at c2 (<anonymous>:21:15)
at test (<anonymous>:32:2)
Shouldn't the calling functions be part of the stack trace?
I tested this code in Google Chrome.
Async stack traces (the ones you get in production) only work with async functions so when you have a function that isn't async and just uses promises the chain won't stitch. You can read more on the implementation in the design document the fix fortunately is pretty simple:
// the function has to be async
async function a() {
// isolate areas that have to use raw promises
await new Promise((resolve, reject)=>{
setTimeout(()=>resolve(), 2000);
});
// throw the error from inside the function
throw new Error('a');
}
Which happily logs:
Error: a
at a (<anonymous>:6:11)
at async b (<anonymous>:10:5)
at async c (<anonymous>:14:5)
at async test (<anonymous>:23:5)
I could be wrong but I believe its because you create an anonymous function within setTimeout, which would then be thrown for the error.
Maybe not the cleanest, but for every Error I put in a logPrefix, and do something like the below. Just means you can easily debug an error.
const logPrefix = '[my-function-name]'
throw new Error(`${logPrefix} - The error maybe with ${error} injected`)
If my function is within a class or something I might do the below
const logPrefix = '[className.methodName]'