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JavaScript Scope — exercises and bug fixes

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

    Read a global variable

    easy10 min

    Read a variable declared outside the function from inside it.

  2. 2

    Keep a variable local

    easy10 min

    Show that a variable declared inside a function does not exist outside.

  3. 3

    Walk the scope chain

    easy10 min

    Join a value from each of three nested scopes with a dash.

  4. 4

    Shadow an outer variable

    easy10 min

    Declare a variable inside a function with the same name and show the outer one is untouched.

  5. 5

    Pass instead of sharing

    medium10 min

    Pass a value into a function rather than reading a global, and show the result.

Find the bug(5)

  1. 1

    Fix the variable read out of scope

    easy8 min

    The variable only exists inside the function.

  2. 2

    Fix the shadowed value

    easy8 min

    The inner variable hides the outer one, so the wrong value is returned.

  3. 3

    Fix the broken scope chain

    easy8 min

    The inner function cannot see a variable declared after it runs.

  4. 4

    Fix the hidden global dependency

    easy8 min

    The function reads an outside rate, so changing it changes the answer.

  5. 5

    Fix the outer variable overwritten

    easy8 min

    The function changes the global instead of using its own copy.

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