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JavaScript Arrow Functions — exercises and bug fixes

5 hands-on exercises and 5 find-the-bug challenges for the JavaScript Arrow 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 an arrow function

    easy10 min

    Write an arrow function that doubles a number. Show it for 25.

  2. 2

    Use an implicit return

    easy10 min

    Write the same doubling function in one line with no braces. Show it for 33.

  3. 3

    Two parameters

    easy10 min

    Write an arrow function that adds two numbers. Show 8 plus 9.

  4. 4

    An arrow as a callback

    easy10 min

    Use an arrow function with map to square each number, then join with commas.

  5. 5

    Return an object

    medium10 min

    Return an object from a one-line arrow function and show its name.

Find the bug(5)

  1. 1

    Fix the missing arrow

    easy8 min

    An arrow function needs the arrow between the parameters and the body.

  2. 2

    Fix the braces without return

    easy8 min

    With braces the function must return explicitly.

  3. 3

    Fix the missing brackets

    easy8 min

    With two parameters the round brackets are required.

  4. 4

    Fix the object read as a body

    easy8 min

    Without round brackets the braces are treated as a function body.

  5. 5

    Fix the arrow used as a method

    easy8 min

    An arrow function has no this, so it cannot see the object.

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