Beginner
Type the Callback
mapNumbers calls a function on every number and collects the results. Type the callback fn as a function that takes a number and returns a string, and give the function a return type.
A callback that takes a string, or that returns a number, must be rejected.
What Check tests
- Your code has no type errors
- The console prints
[ '#1', '#2', '#3' ] - A callback taking a string is rejected
- A callback returning a number is rejected
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