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TypeScript 的类型体操笔记，温故知新。
ReplaceKeys、Remove Index Signature、Percentage Parser
AnyOfPython 中 any 函数。类型接收一个数组，如果数组中任一个元素为真，则返回 true，否则返回 false。如果数组为空，返回 false。type Falsy = 0 | "" | false | [] | { [key: string]: never } | undefined | null;
type AnyOf<T extends readonly any[]> = T[number] extends Falsy ? false : true;
IsNeverIsNever, which takes input type T. If the type of resolves to never, return true, otherwise false.// For example:
type A = IsNever<never>; // expected to be true
type B = IsNever<undefined>; // expected to be false
type C = IsNever<null>; // expected to be false
type D = IsNever<[]>; // expected to be false
type E = IsNever<number>; // expected to be false
type IsNever<T> = [T] extends [never] ? true : false;
// or
type IsNever<T> = T[] extends never[] ? true : false;
IsUnionIsUnion, which takes an input type T and returns whether T resolves to a union type.// For example:
type case1 = IsUnion<string>; // false
type case2 = IsUnion<string | number>; // true
type case3 = IsUnion<[string | number]>; // false
type IsUnion<T, C = T> = [T] extends [never] ? false : T extends C ? ([C] extends [T] ? false : true) : false;
// 同
type IsUnion<T, C = T> = [T] extends [never] ? false : T extends T ? ([C] extends [T] ? false : true) : false;
ReplaceKeysReplaceKeys, that replace keys in union types, if some type has not this key, just skip replacing, A type takes three arguments.// For example:
type NodeA = {
type: "A";
name: string;
flag: number;
};
type NodeB = {
type: "B";
id: number;
flag: number;
};
type NodeC = {
type: "C";
name: string;
flag: number;
};
type Nodes = NodeA | NodeB | NodeC;
type ReplacedNodes = ReplaceKeys<Nodes, "name" | "flag", { name: number; flag: string }>; // {type: 'A', name: number, flag: string} | {type: 'B', id: number, flag: string} | {type: 'C', name: number, flag: string} // would replace name from string to number, replace flag from number to string.
type ReplacedNotExistKeys = ReplaceKeys<Nodes, "name", { aa: number }>; // {type: 'A', name: never, flag: number} | NodeB | {type: 'C', name: never, flag: number} // would replace name to never
type ReplaceKeys<U, T, Y> = {
[K in keyof U]: K extends T ? (K extends keyof Y ? Y[K] : never) : U[K];
};
Remove Index SignatureRemoveIndexSignature<T> , exclude the index signature from object types.// For example:
type Foo = {
[key: string]: any;
foo(): void;
};
type A = RemoveIndexSignature<Foo>; // expected { foo(): void }
type RemoveIndexSignature<T, P = PropertyKey> = {
[K in keyof T as P extends K ? never : K extends P ? K : never]: T[K];
};
Percentage Parser匹配的结果由三部分组成，分别是：[正负号, 数字, 单位]，如果没有匹配，则默认是空字符串。
type CheckPrefix<T> = T extends "+" | "-" ? T : never;
type CheckSuffix<T> = T extends `${infer P}%` ? [P, "%"] : [T, ""];
type PercentageParser<A extends string> = A extends `${CheckPrefix<infer L>}${infer R}` ? [L, ...CheckSuffix<R>] : ["", ...CheckSuffix<A>];
type PercentageParser<A extends string> = A extends `${infer L}${infer R}`
? L extends "+" | "-"
? R extends `${infer N}%`
? [L, N, "%"]
: [L, R, ""]
: A extends `${infer N}%`
? ["", N, "%"]
: ["", A, ""]
: ["", "", ""];