Working without blocking.
WHAT THE PATTERNS ARE
Callbacks, the original approach Promises The modern syntax reading sequentially
WHAT TO USE
The modern syntax, with promises underneath.
WHY
Nested callbacks become unreadable quickly.
WHAT TO ALWAYS DO
Handle failure.
WHY
An unhandled rejection can terminate the process in current versions.
WHAT TO WRAP
Anything that can fail, which is everything doing input or output.
WHAT TO BE CAREFUL WITH
Awaiting sequentially where operations are independent.
WHY
It makes three parallel operations take three times as long.
WHAT TO DO INSTEAD
Run them concurrently and await all.
WHAT TO BE CAREFUL WITH IN LOOPS
Awaiting inside a loop, serialising work unnecessarily.
WHAT TO SET
Timeouts on every external call.
WHY
A hanging dependency otherwise exhausts your capacity.
WHAT TO IMPLEMENT FOR FLAKY DEPENDENCIES
Retries with increasing delay, and a limit.
WHAT TO AVOID
Retrying operations that are not safe to repeat.
