NEW ANSWER FOR TYPESCRIPT 4.1+ Welcome back! Now that TypeScript 4.1 has introduced template literal types and the Uppercase/Lowercase intrinsic string mapping types, we can now answer this question without needing regular expression types. There are two main approaches. The “brute force” approach makes heavy use of recursive conditional types and unions to turn your … Read more
Yeah, you can test for any: type IfAny<T, Y, N> = 0 extends (1 & T) ? Y : N; type IsAny<T> = IfAny<T, true, never>; type A = IsAny<any> // true type B = IsAny<number> // never type C = IsAny<unknown> // never type D = IsAny<never> // never The explanation for this is … Read more
The type is just Event. Relevant information is on e.target property.
In TypeScript, a homomorphic mapped type is specifically a type in which the compiler recognizes that you are mapping the properties of an existing object type. In such cases, the output object type will have the same readonly and/or optional (?) property modifiers on its properties as the ones on the input type do. This … Read more
The error message you are describing occurs in a declaration file. To make this work, you need remove the semi-colon at the end of your interface declaration: interface DependData { [key: string]: string; } The extra semi-colon is causing an empty statement to be parsed in addition to the interface declaration, thus giving that error … Read more
You can use the buit-in Pick type to get part of an interface : type PostsInfoWithoutConent= Pick<PostsInfo, “id” | “title”> If you just want to exclude one property you might be better off defining the the Omit type and use that type Diff<T extends string, U extends string> = ({[P in T]: P } & … Read more
Quite easy. someArray.indexOf you know that this is a function, which is also an object and can have properties. By doing someArray.indexOf[someObject], you are trying to reach the property with the key valued to the value of someObject. Of course, it is not defined on the indexOf function, so it returns undefined. Quick example that … Read more
In my case it was @types/node that was triggering the error on AbortSignal type declaration. In some of my projects, a fresh (re)install of @types/node to latest version fixed the bug In some others, I have uninstalled @types/node which was probably duplicated somewhere. Doing so didn’t change anything at my dev workflow (not sure why … Read more
UPDATE: VS Code now supports this functionality out of the box. Just add the interface, the compiler will highlight the controller with red, right click on the light bulb on the left and click implement interface. Enjoy!
Presumably you’re unhappy about the following error: const fooBad = ({ bar }?: { bar?: boolean }) => {}; // error! // ┌──────────> ~~~~~~~~~~~~~~~~~~~~~~~~~~~ // A binding pattern parameter cannot be optional in an implementation signature. Which makes sense, because you can’t destructure undefined. What you can do, in TypeScript, is to use a default … Read more