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error-handling-try-catch

Error handling

Last reviewed May 28, 2026 Content v20260528
Track mode
client_javascript
Means
In-browser JS
Reading
~1 min
Level
intermediate

This lesson

This lesson teaches Error handling—the ideas, syntax, and habits you need before moving on in JavaScript.

Without a solid grasp of Error handling, you will repeat mistakes in JavaScript exercises and on real pages or scripts.

You will apply Error handling in contexts like: Browsers, Node.js services, edge workers, and tooling ecosystems (bundlers, test runners).

Run JavaScript in the in-browser sandbox, use the terminal output panel, and verify with MCQs.

Toward the end of the track—use it to consolidate patterns before the capstone or summary lessons.

Use try/catch/finally for sync errors and await failures. Throw Error objects with messages.

Custom errors

Subclass Error for domain failures—stack traces aid debugging.

User-facing

Log full error server-side; show generic message client-side—no stack traces to users.

Important interview questions and answers

  1. Q: throw string?
    A: Avoid—throw Error for stack traces.
  2. Q: finally?
    A: Runs always—cleanup resources.

Self-check

  1. Why try/catch with await?
  2. What belongs in finally?

Tip: Re-run the playground code for error-handling-try-catch and tweak one line before the MCQs.

Interview prep

throw Error?

Preserves stack trace for debugging.

Interview tip Lesson completion confidence

Can you explain this lesson in 30 seconds without reading notes?

Not saved yet.

Playground

Runs in your browser in a sandboxed frame. Backend runners appear when this track’s profile allows them.

Check yourself

Multiple choice — immediate feedback.

Discussion

Past discussion is visible to everyone. Only logged-in users can post comments and replies.

Starter discussion topics

  • What would you log to verify this behavior?
  • What breaks if you run this before the DOM is ready?

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