What this snippet does
The constraint ensures the key exists, failing compilation if an arbitrary string is passed.
Expected output
Compile Error: Argument of type '"b"' is not assignable to parameter of type '"a"'.
Why practise typing this
Typing generics code builds muscle memory for the symbols and indentation TypeScript uses most, which prose-based typing tests never cover. DevType measures your words per minute and accuracy on this snippet and tracks the individual characters you mistype, so later lessons can target them.
More TypeScript practice
- Writing a basic identity functionGenerics · intermediate
- Creating a generic API fetcherGenerics · intermediate
- Assuming generic types have specific methodsGenerics · intermediate
- Defining a generic box interfaceGenerics · intermediate
- Defining a generic pagination responseGenerics · intermediate
- Using an interface without providing type argumentsGenerics · intermediate