Question:
I’m having trouble finding out why my code never ends execution and gets stuck. It logsdone
before doing anything in the async run()
block. The code just hangs with an output of:Answer:
According to the MongoDB NodeJS driver documentation, cursors (inheriting from AbstractCursor) have an[asyncIterator]
symbol. An object that has that symbol implements a function that allows you to use them in a for await...of
loop:for await...of
loop will fetch one item from the cursor, run whatever is in its body, then repeat until the cursor is exhausted. You can use break
, continue
, try {} catch {}
in the body, just like regular loops.This will process all items after each other in series, which seems to be what you were aiming for.
If you want to run things in parallel, use a library that can take the AsyncIterator and turn it into batches, then process (for example) 5 at a time until it’s exhausted. But doing it in series is probably fast enough, it’s easier and less complex.
If you have better answer, please add a comment about this, thank you!