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JavaScript Promises — exercises and bug fixes

5 hands-on exercises and 5 find-the-bug challenges for the JavaScript Promises lesson. Every one is checked automatically in the browser — write the code, run it, and the tests tell you what still fails.

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Exercises(5)

  1. 1

    Create and resolve a promise

    easy10 min

    Make a promise that resolves with a name and report it.

  2. 2

    Reject a promise

    easy10 min

    Reject a promise and report the reason with catch.

  3. 3

    Use Promise.resolve

    easy10 min

    Use a ready-made resolved promise and report its value.

  4. 4

    Show it settles once

    easy10 min

    Resolve twice and show only the first value is kept.

  5. 5

    Show then runs later

    medium10 min

    Report the order of a synchronous line and a then handler.

Find the bug(5)

  1. 1

    Fix the promise never resolved

    easy8 min

    Nothing calls resolve, so the handler never runs.

  2. 2

    Fix then used for a rejection

    easy8 min

    A rejected promise is handled by catch, not by then.

  3. 3

    Fix the value read outside the handler

    easy8 min

    The value only exists inside then.

  4. 4

    Fix reject used where resolve belongs

    easy8 min

    The work succeeded, so the promise should resolve.

  5. 5

    Fix then called on the value

    easy8 min

    then belongs to the promise, not to what it resolves with.

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