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JavaScript NaN — exercises and bug fixes

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

    Produce a NaN

    easy10 min

    Convert text that is not a number and report the result.

  2. 2

    Report its type

    easy10 min

    Report what typeof gives for NaN.

  3. 3

    Show it is not equal to itself

    easy10 min

    Compare NaN with itself and report the outcome.

  4. 4

    Check for it properly

    easy10 min

    Use Number.isNaN to detect a failed conversion.

  5. 5

    Guard a calculation

    medium10 min

    Return a message rather than letting NaN escape.

Find the bug(5)

  1. 1

    Fix the equality check for NaN

    easy8 min

    NaN is never equal to itself, so equality cannot detect it.

  2. 2

    Fix the global isNaN

    easy8 min

    The global isNaN converts first, so it answers a different question.

  3. 3

    Fix the unguarded calculation

    easy8 min

    A failed conversion spreads NaN through the whole sum.

  4. 4

    Fix typeof used to detect NaN

    easy8 min

    typeof NaN is number, so it cannot identify it.

  5. 5

    Fix the total ruined by one value

    easy8 min

    One unconvertible entry turns the whole total into NaN.

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