· 148 words · 1 min
利用 ts 自带的 Uppercase
工具类型。
type Capitalize<S extends string> =
S extends `${infer First}${infer Rest}`
? `${Uppercase<First>}${Rest}`
: S;
type result = Capitalize<'captainOfPhB'>; // CaptainOfPhB
never
的索引会在生成新的索引类型时被去掉。
type FilterByValueType<Obj extends Record<string, any>, ValueType> = {
[Key in keyof Obj as ValueType extends Obj[Key] ? Key : never] : Obj[Key]
}
interface Person {
name: string;
age: number;
hobby: string[];
}
type result = FilterByValueType<Person, string | number>; // { name: string; age: number }
type IsEqual<A, B> = (A extends B ? 1 : 2) extends (B extends A ? 1 : 2) ? true : false;
type BuildArray<Length extends number, Ele = unknown, Arr extends unknown[] = []> =
Arr['length'] extends Length
? Arr
: BuildArray<Length, Ele, [...Arr, Ele]>;
type result = BuildArray<3>; // [unknown, unknown, unknown]