| BASIC |
string, number, boolean, union |
| TYPE MANIPULATION |
generics, conditionals, keys, infer, mapped types + modifiers, index access |
| UTILITY TYPES |
exclude, extract，pick, omit |
| OBJECT TYPES |
optional properties |
Use generics, unions, conditionals#
type IsTruthy<T> = T extends null | undefined | false | 0 | "" ? false : true;
// equals
type IsTruthy<Y> =
if: T extends null | undefined | false | 0 | ""
then: false
else: true;
Use utility types#
utility types 是一类TS提供的MappedTypes，常用如下：
- Exclude, Returns the provided union, minus any union items to exclude.
- Pick, Return a new type from the provided type with the keys.
type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>
type ValidDoubleObject<T> = T extends { a: infer U; b: infer U } ? U : never;
// IDE Loose Autocomplete，加上 （string & {}）; 只加 string，ModelNames就是string，Autocomplete会失败；
type ModelNames = "gpt-4o" | "o3-mini" | "claude-sonnet-latest" | (string & {});
const model: ModelNames = "others"; // 此处可以显示正确的 Autocomplete
Use mapped types#
// -? means remove optional modifier(去掉 Optional 标识).
type MappedValidType<T> = {[K in keyof T]-?: true};
type ValidKeyUnion<T> = {[K in keyof T]-?: true}[keyof T];
type ValidKeys<T> = {
[K in keyof T]-?: (Exclude<T[K], null>) extends { a: infer U; b: infer U }
? IsTruthy<U> extends true ? K : never
: never
}[keyof T]
// 对于 Complex Type，运用该 util 可使得 type 一目了然
type Prettify<T> = { [K in keyof T]: T[K]} & {};