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JavaScript preventDefault — exercises and bug fixes

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

    Stop a link navigating

    easy10 min

    Cancel the link and report that the page stayed.

  2. 2

    Stop a form reloading

    easy10 min

    Cancel the submit and report that it was handled.

  3. 3

    Check it was prevented

    easy10 min

    Report the value of defaultPrevented after cancelling.

  4. 4

    Stop propagation

    easy10 min

    Stop the click reaching the box and report handled here.

  5. 5

    Filter by target instead

    medium10 min

    Handle only the button, without stopping propagation.

Find the bug(5)

  1. 1

    Fix preventDefault called without brackets

    easy8 min

    It is a method and must be called.

  2. 2

    Fix stopPropagation used to cancel an action

    easy8 min

    Stopping the travel does not stop the browser navigating.

  3. 3

    Fix preventDefault used to stop the bubble

    easy8 min

    The click should not reach the box, which needs stopPropagation.

  4. 4

    Fix return false used to cancel

    easy8 min

    Returning false does nothing in an addEventListener handler.

  5. 5

    Fix the unnecessary stopPropagation

    easy8 min

    Checking the target is enough, and leaves other handlers working.

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