Eye Training · Resources and Cleanup

Everything you open, take or start must be given back on every path out: success, early return, thrown error and shutdown.

Part 2 · Surface 24. Bug counts are hidden and some snippets are clean. See Start Here for how to use these drills.

J · The basics

Bug hunt

J · Sync button

Bug count hidden, and some snippets are clean. Click every line you think is wrong (or none), then check.

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Bug hunt

J · Find a user

Bug count hidden, and some snippets are clean. Click every line you think is wrong (or none), then check.

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Bug hunt

J · Find an order

Bug count hidden, and some snippets are clean. Click every line you think is wrong (or none), then check.

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M · Three years in, these should jump out

Bug hunt

M · Image preview

Bug count hidden, and some snippets are clean. Click every line you think is wrong (or none), then check.

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Bug hunt

M · PDF conversion

Bug count hidden, and some snippets are clean. Click every line you think is wrong (or none), then check.

0:00 / 2 min

Bug hunt

M · Cache sweeper

Bug count hidden, and some snippets are clean. Click every line you think is wrong (or none), then check.

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Bug hunt

M · Thumbnails

Bug count hidden, and some snippets are clean. Click every line you think is wrong (or none), then check.

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S · Where seniors stand out

Bug hunt

S · Transfer

Bug count hidden, and some snippets are clean. Click every line you think is wrong (or none), then check.

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Bug hunt

S · Shutdown

Bug count hidden, and some snippets are clean. Click every line you think is wrong (or none), then check.

0:00 / 2 min

Bug hunt

S · Compress a log

Bug count hidden, and some snippets are clean. Click every line you think is wrong (or none), then check.

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What your eye checks

Whenever code opens, takes or starts something, find where it's given back, then ask:

Is it released on every path? Early returns and thrown errors skip the last line. Releases belong in finally.
Does a flag or lock get reset on failure? A stuck busy is a resource leak too.
Is a transaction rolled back? Releasing a connection isn't enough if the transaction is still open.
Is there a limit? Threads, connections, child processes and open files need a pool or a cap.
Does importing it start anything? Timers and sockets started at import time keep the process alive.
Are names unique? Temp files and keys built from Date.now() collide.
Does shutdown wait? Stop taking work, finish what's in flight, then close what it uses.
Is there a helper that does the cleanup for you? pool.query, pipeline, fs.rm with force.

Tells

You see	Ask
`pool.connect()`	Where's `release`, and is it in `finally`?
`return` between acquire and release	Released on this path?
`busy = true` … `busy = false`	What if it throws in between?
`BEGIN` without a `ROLLBACK`	What does the next user of this connection get?
`URL.createObjectURL`	Where's `revokeObjectURL`?
`new Worker`, `spawn`, `new Client` per request	What's the limit?
`setInterval` at the top of a module	Does the process ever exit?
`tmpdir()` + `Date.now()`	Unique? Deleted on failure?
`server.close()` not awaited	Are requests in flight dropped?

Go deeper

try / catch / finally: which failures escape and what finally guarantees
Streams and streaming data: backpressure and stream errors
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