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前言

TypeScript 越来越火，现在很多前端团队都使用它，因此咱们前端码农要想胜任以后的前端工作，就要更加熟悉它。

入门练手题

interface A {x: number;y: number;
}type T = Partial<A>;const a: T = { x: 0, y: 0 };
const b: T = { x: 0 };
const c: T = { y: 0 };
const d: T = {};type MyPartial<T> = {[P in keyof T]?: T[P];
};interface B {x?: number;y: number;
}type T0 = Required<B>;const a0: T0 = { x: 0, y: 0 };type MyRequired<T> = {[P in keyof T]-?: T[P];
};interface C {x?: number;y: number;
}type T1 = Readonly<C>;const a1: T1 = { x: 0, y: 0 };// a1.x=1type MyReadonly<T> = {readonly [P in keyof T]: T[P];
};interface Cat {age: number;gender: string;
}type CatName = "seraph" | "ashe" | "ahri";const cats: Record<CatName, Cat> = {seraph: { age: 10, gender: "male" },ashe: { age: 5, gender: "female" },ahri: { age: 16, gender: "female" },
};/* 在 TypeScript 中，当你看到 K extends keyof any 这样的表达时，
它的作用是约束类型 K 为一个有效的类型，可以作为对象的键。
这里的 keyof any 是指所有可能的 JavaScript 值的键的联合类型。
简单来说，keyof any 通常等价于 string | number | symbol ，
因为在 JavaScript 中，对象的键可以是这三种类型。
你可以使用 string，number 或者 symbol 作为对象属性的键。 */type MyRecord<K extends keyof any, T> = {[P in K]: T;
};interface Todo {title: string;description: string;done: boolean;
}type TodoPreview = Pick<Todo, "title" | "done">;const todo: TodoPreview = {title: "play games",done: false,
};type MyPick<T, K extends keyof T> = {[P in K]: T[P];
};type E0 = Exclude<"a" | "b", "a">;type E1 = Exclude<string | number | (() => void), Function>;type MyExclude<T, U> = T extends U ? never : T;interface Todos {title: string;desc: string;done: boolean;no: number;
}type TodoPre = Omit<Todos, "desc">;const todopre: TodoPre = {title: "play",done: false,no: 2,
};type TodoInfo = Omit<Todos, "desc" | "no">;const todoInfo: TodoInfo = {title: "play",done: false,
};type MyOmit<T, K extends keyof any> = Pick<T, Exclude<keyof T, K>>;type E = Extract<"a" | "b", "a" | "f">;type E3 = Extract<string | number | (() => void), Function>;type MyExtrat<T, U> = T extends U ? T : never;declare function f(args: { a: number; b: string }): void;type P0 = Parameters<() => string>; // []type P1 = Parameters<(s: string) => void>; // [s: string]type P2 = Parameters<<T>(arg: T) => T>; // [arg: unknown]type P3 = Parameters<typeof f>;type MyParameters<T extends (...args: any) => any> = T extends (...args: infer P
) => any? P: never;type R = ReturnType<() => void>;const add = (x: number, y: number): number => {return x + y;
};type R1 = MyReturnType<typeof add>;type MyReturnType<T extends (...args: any) => any> = T extends (...args: any
) => infer R? R: any;