TypeScript 高级技巧

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interface Point {
x: number;
y: number;
}
// type keys = "x" | "y"
type keys = keyof Point;
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const data = {
a: 3,
hello: 'world'
}
function get(o: object, name: string) {
return o[name]
}
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function get<T extends object, K extends keyof T>(o: T, name: K): T[K] {
return o[name]
}
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type Partial<T> = {
[P in keyof T]?: T[P];
};
type Pick<T, K extends keyof T> = {
[P in K]: T[P];
};
interface User {
id: number;
age: number;
name: string;
};
// 相当于: type PartialUser = { id?: number; age?: number; name?: string; }
type PartialUser = Partial<User>
// 相当于: type PickUser = { id: number; age: number; }
type PickUser = Pick<User, "id" | "age">
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T extends U ? X : Y
type isTrue<T> = T extends true ? true : false
// 相当于 type t = false
type t = isTrue<number>
// 相当于 type t = false
type t1 = isTrue<false>
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type Exclude<T, U> = T extends U ? never : T;
// 相当于: type A = 'a'
type A = Exclude<'x' | 'a', 'x' | 'y' | 'z'>
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type Omit<T, K extends keyof any> = Pick<T, Exclude<keyof T, K>>;
interface User {
id: number;
age: number;
name: string;
};
// 相当于: type PickUser = { age: number; name: string; }
type OmitUser = Omit<User, "id">
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const a: number = 3
// 相当于: const b: number = 4
const b: typeof a = 4
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import logger from './logger'
import utils from './utils'
interface Context extends KoaContect {
logger: typeof logger,
utils: typeof utils
}
app.use((ctx: Context) => {
ctx.logger.info('hello, world')
// 会报错，因为 logger.ts 中没有暴露此方法，可以最大限度的避免拼写错误
ctx.loger.info('hello, world')
})
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app.use(async (ctx, next) => {
try {
await next();
} catch (err) {
let code = 'BAD_REQUEST'
if (err.isAxiosError) {
code = `Axios-${err.code}`
} else if (err instanceof Sequelize.BaseError) {
}
ctx.body = {
code
}
}
})
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if ((err as AxiosError).isAxiosError) {
code = `Axios-${(err as AxiosError).code}`
}
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function isAxiosError (error: any): error is AxiosError {
return error.isAxiosError
}
if (isAxiosError(err)) {
code = `Axios-${err.code}`
}
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export function isType(type: any): type is GraphQLType;
export function isScalarType(type: any): type is GraphQLScalarType;
export function isObjectType(type: any): type is GraphQLObjectType;
export function isInterfaceType(type: any): type is GraphQLInterfaceType;
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interface A {
a: number;
b: number;
};
type B {
a: number;
b: number;
}
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interface A {
a: number;
}
interface A {
b: number;
}
const a: A = {
a: 3,
b: 4
}
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interface Dictionary<T> {
[index: string]: T;
};
interface NumericDictionary<T> {
[index: number]: T;
};
const data:Dictionary<number> = {
a: 3,
b: 4
}
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// 使用 object 维护常量
const enum TODO_STATUS {
TODO = 'TODO',
DONE = 'DONE',
DOING = 'DOING'
}
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// 使用 const enum 伟华常量
const enum TODO_STATUS {
TODO = 'TODO',
DONE = 'DONE',
DOING = 'DOING'
}
function todos (status: TODO_STATUS): Todo[];
todos(TODO_STATUS.TODO)
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{
"typescript.tsdk": "node_modules/typescript/lib"
}
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