[英]how to remove properties and promisify method via mapped type in TypeScript
[英]how to remove properties via mapped type in TypeScript
這是代碼
class A {
x = 0;
y = 0;
visible = false;
render() {
}
}
type RemoveProperties<T> = {
readonly [P in keyof T]: T[P] extends Function ? T[P] : never//;
};
var a = new A() as RemoveProperties<A>
a.visible // never
a.render() // ok!
我想通過 RemoveProperties 刪除“visible / x / y”屬性,但我只能用 never 替換它
您可以使用與Omit
類型相同的技巧:
// We take the keys of P and if T[P] is a Function we type P as P (the string literal type for the key), otherwise we type it as never.
// Then we index by keyof T, never will be removed from the union of types, leaving just the property keys that were not typed as never
type JustMethodKeys<T> = ({[P in keyof T]: T[P] extends Function ? P : never })[keyof T];
type JustMethods<T> = Pick<T, JustMethodKeys<T>>;
type Methods<T> = { [P in keyof T as T[P] extends Function ? P : never]: T[P] };
type A_Methods = Methods<A>; // { render: () => void; }
當
as
子句中指定的類型解析為never
,不會為該鍵生成任何屬性。 因此,as
子句可以用作過濾器 [.]
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