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JavaScript Promise Chaining — exercises and bug fixes

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

    Chain two steps

    easy10 min

    Multiply a value in one step and report it in the next.

  2. 2

    Build a string across steps

    easy10 min

    Add a letter in each step and report the result.

  3. 3

    Wait for another promise

    easy10 min

    Return a promise from a step so the chain waits for it.

  4. 4

    Catch at the end

    easy10 min

    Throw in the middle of a chain and catch it at the end.

  5. 5

    Recover and continue

    medium10 min

    Catch a rejection, return a value, and carry on down the chain.

Find the bug(5)

  1. 1

    Fix the missing return

    easy8 min

    Without a return the next step receives undefined.

  2. 2

    Fix the nested then

    easy8 min

    Nesting rebuilds callback hell; the promise should be returned instead.

  3. 3

    Fix the catch placed too early

    easy8 min

    A catch before the failing step cannot catch it.

  4. 4

    Fix the steps run separately

    easy8 min

    Calling then twice on the same promise does not chain them.

  5. 5

    Fix the value used after the chain

    easy8 min

    The chain has not finished when the line below runs.

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