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JavaScript Pure Functions — exercises and bug fixes

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

    Write a pure function

    easy10 min

    Write a pure add function and call it twice with the same values, joining the answers.

  2. 2

    Take everything as a parameter

    easy10 min

    Pass the tax rate in rather than reading an outside variable. Show 100 at 1.2.

  3. 3

    Return a new array

    easy10 min

    Add a value without changing the original array. Show the original length.

  4. 4

    Copy before sorting

    easy10 min

    Sort a copy so the original order is kept. Show the original joined by commas.

  5. 5

    A pure total

    medium10 min

    Add up a list with reduce without changing it, and show the total.

Find the bug(5)

  1. 1

    Fix the outside variable

    easy8 min

    Reading an outside rate makes the answer change unexpectedly.

  2. 2

    Fix the array that was changed

    easy8 min

    push changes the array that was passed in.

  3. 3

    Fix the sort that reorders the original

    easy8 min

    sort changes the array it is called on.

  4. 4

    Fix the counter side effect

    easy8 min

    The function changes a variable outside itself.

  5. 5

    Fix the object that was mutated

    easy8 min

    The function changes the object it was given.

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