FAQ: Custom Types - Function Types

This community-built FAQ covers the “Function Types” exercise from the lesson “Custom Types”.

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FAQs on the exercise Function Types

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The mathTutor function makes use of the callback function’s name property. This property is not defined as part of the function type following the solution/hint given.

index.ts:13:55 - error TS2339: Property 'name' does not exist on type 'OperatorFunction'.

13   console.log("Let's learn how to", operationCallback.name,'!');

Hint from the exercise:

To define the type alias, you will write type OperatorFunction = (arg0:<something>, arg1:<something else>) => <thing> . What should be the values of <something> , <something else> , and <thing> ?

Am I missing something? How can I define a function type for a callback function using arrow functions (which are anonymous) and use the callback function’s name property?

This question was confusing to me as well. The only thing we’re typing in step 3 is the parameter of mathTutor. The OperatorCallback type is referring to that parameter alone. I was trying to type mathTutor itself, which is not what they want you to do. If you do like the hint says, and apply it to operationCallback it works