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JavaScript Date Pitfalls — exercises and bug fixes

5 hands-on exercises and 5 find-the-bug challenges for the JavaScript Date Pitfalls 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

    See a rollover

    easy10 min

    Build January 32 and report the month number it lands on.

  2. 2

    Detect an invalid date

    easy10 min

    Report that an unparseable string gives an invalid date.

  3. 3

    Write a validity check

    easy10 min

    Write a helper and use it on a good date.

  4. 4

    Protect the caller's date

    easy10 min

    Add a week to a copy and report the original day.

  5. 5

    See February roll over

    medium10 min

    Build February 30 and report the month it lands on.

Find the bug(5)

  1. 1

    Fix the invalid date left unchecked

    easy8 min

    An invalid date gives NaN rather than throwing.

  2. 2

    Fix the validity check using equality

    easy8 min

    An invalid date is never equal to NaN.

  3. 3

    Fix the rollover assumed to throw

    easy8 min

    An out-of-range day rolls over silently.

  4. 4

    Fix the helper changing its argument

    easy8 min

    The caller's date must not be modified.

  5. 5

    Fix the month passed as a human number

    easy8 min

    Passing 12 for December rolls into the next year.

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