- 18Use TypeScript's Mapped Types and Template Literal Types Together6m 12s
Use TypeScript's Mapped Types and Template Literal Types Together
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In this final lesson, we're going to dive deep into a more complex example in which we combine mapped types, key remapping, template literal types, and indexed access types to statically type a highly dynamic JavaScript function in TypeScript.
Why do we need the "TKey in string"? Why does TypeScript say it can be 'string | number | symbol' even though we said TObj extends Record<string, unknown>? Thanks for the course :)
Enrico I think those are the primitive types (string | number | symbol) sans boolean, so I think by adding the intersection type TKey in string & keyof TObj... it denotes that we are filtering(?) TKey, otherwise of types string | number | symbol | keyof TObj, on the basis of whether a corresponding key is of type string or not. All non-string keys get 86'd (discarded) by incorporating this intersection.
Please correct me if my understanding is off
Actually, after thinking on it, it seems that it is actually coercing the type of TKey to string, not necessarily filtering them