如何在React项目中使用TypeScript

本文主要记录我如何在React项目中优雅的使用TypeScript，来提高开发效率及项目的健壮性。

项目目录及ts文件划分

由于我在实际项目中大部分是使用umi来进行开发项目，所以使用umi生成的目录来做案例。

.
├── README.md
├── global.d.ts
├── mock
├── package.json
├── src
│   ├── assets
│   ├── components
│   │   └── PublicComA
│   │   ├── index.d.ts
│   │   ├── index.less
│   │   └── index.tsx
│   ├── layouts
│   ├── models
│   ├── pages
│   │   ├── PageA
│   │   │   ├── index.d.ts
│   │   │   ├── index.less
│   │   │   └── index.tsx
│   │   ├── index.less
│   │   └── index.tsx
│   └── utils
├── tsconfig.json
├── typings.d.ts
└── yarn.lock

在项目根目录下有typings.d.ts和global.d.ts这两个文件, 前者我们可以放置一些全局的导出模块,比如css,less, 图片的导出声明；后者可以放一些全局声明的变量, 接口等, 比如说window下全局变量的声明等。如下：

// typings.d.ts
declare module '*.css';
declare module '*.less';
declare module "*.png";
declare module "*.jpeg";
declare module '*.svg' {export function ReactComponent(props: React.SVGProps<SVGSVGElement>): React.ReactElementconst url: stringexport default url
}

// global.d.ts
interface Window {helloWorld: () => void;
}

接下来介绍一下src目录：

assets 存放静态资源如图片/视频/音频等, 参与webpack的打包过程
layouts 存放公共布局
components 存放全局公共组件
models dva的models文件夹
pages 存放页面的目录, 内部可以有页面组件components, 结构类似于全局的components
utils 存放js工具库, 请求库等公共js文件

在pages和components中有存放当前组件/页面所需要的类型和接口声明的index.d.ts。另外如models中的文件由于是每个model私有类型和接口声明，所以可以直接在文件内部去声明。具体的目录规划如上，可以根据实际项目来做更合理的划分。

在项目中使用TypeScript具体实践

组件声明

1.函数组件推荐使用React.FC<P={}>来表示函数类型，当使用该类型定义组件时，props中会默认带有children属性。

interface IProps {count: number
}

const App: React.FC<IProps> = (props) => {const {count} = props;return (<div className="App"><span>count: {count}</span></div>);
}

2.类组件类组件接受两个参数，第一个是props的定义，第二个是state的定义，如果使用React.PureComponent<P, S={} SS={}>定义组件，则还有第三个参数，表示getSnapshotBeforeUpdate的返回值。

interface IProps {name: string;
}

interface IState {count: number;
}

class App extends React.Component<IProps, IState> {state = {count: 0};render() {return (<div>{this.state.count}{this.props.name}</div>);}
}

React Hooks使用

useState

声明定义：

function useState<S>(initialState: S | (() => S)): [S, Dispatch<SetStateAction<S>>];
// convenience overload when first argument is omitted
	/**
	 * Returns a stateful value, and a function to update it. * * @version 16.8.0 * @see https://reactjs.org/docs/hooks-reference.html#usestate */function useState<S = undefined>(): [S | undefined, Dispatch<SetStateAction<S | undefined>>];/** * An alternative to `useState`. * * `useReducer` is usually preferable to `useState` when you have complex state logic that involves * multiple sub-values. It also lets you optimize performance for components that trigger deep * updates because you can pass `dispatch` down instead of callbacks. * * @version 16.8.0 * @see https://reactjs.org/docs/hooks-reference.html#usereducer */

如果初始值能够体现出类型，那么可以不用手动声明类型，TS会自动推断出类型。如果初始值为null或者undefined则需要通过泛型显示声明类型。如下：

const [count, setCount] = useState(1);

const [user, setUser] = useState<IUser | null>(null);

useRef

声明定义：

 function useRef<T>(initialValue: T): MutableRefObject<T>;
 // convenience overload for refs given as a ref prop as they typically start with a null value
 /** * `useRef` returns a mutable ref object whose `.current` property is initialized to the passed argument * (`initialValue`). The returned object will persist for the full lifetime of the component. * * Note that `useRef()` is useful for more than the `ref` attribute. It’s handy for keeping any mutable * value around similar to how you’d use instance fields in classes. * * Usage note: if you need the result of useRef to be directly mutable, include `| null` in the type * of the generic argument. * * @version 16.8.0 * @see https://reactjs.org/docs/hooks-reference.html#useref */

使用该Hook时，要根据使用场景来判断传入泛型类型，如果是获取DOM节点，则传入对应DOM类型即可；如果需要的是一个可变对象，则需要在泛型参数中包含’| null’。如下：

// 不可变DOM节点，只读
const inputRef = useRef<HTMLInputElement>(null);

// 可变，可重新复制
const idRef = useRef<string | null>(null);
idRef.current = "abc";

useCallback

声明定义：

 function useCallback<T extends (...args: any[]) => any>(callback: T, deps: DependencyList): T;
 /*** `useMemo` will only recompute the memoized value when one of the `deps` has changed.** Usage note: if calling `useMemo` with a referentially stable function, also give it as the input in* the second argument.** ```ts* function expensive () { ... }** function Component () {* const expensiveResult = useMemo(expensive, [expensive])* return ...* }* ```** @version 16.8.0* @see https://reactjs.org/docs/hooks-reference.html#usememo*/

useCallback会根据返回值自动推断出类型，如果传入的参数不指定类型，则会默认为any，所以为了严谨和可维护性，一定要指定入参的类型。也可以手动传入泛型指定函数类型。如下：

// 会自动推导出类型： (a: number, b: number) => number;
const add = useCallback((a: number, b: number) => a + b, [a, b])

// 传入泛型，则指定函数类型
const toggle = useCallback<(a: number) => number>((a: number) => a * 2, [a])

useMemo

声明定义：

function useMemo<T>(factory: () => T, deps: DependencyList | undefined): T; /*** `useDebugValue` can be used to display a label for custom hooks in React DevTools.** NOTE: We don’t recommend adding debug values to every custom hook.* It’s most valuable for custom hooks that are part of shared libraries.** @version 16.8.0* @see https://reactjs.org/docs/hooks-reference.html#usedebugvalue*/

useMemo和useCallback类似，只是定义类型为具体返回值的类型，而不是函数的类型。如下：

// 会自动推导出类型： number;
const add = useCallback((a: number, b: number) => a + b, [a, b])

// 传入泛型，则指定函数类型
const toggle = useCallback<number>((a: number) => a * 2, [a])

useContext

声明定义：

function useContext<T>(context: Context<T>/*, (not public API) observedBits?: number|boolean */): T;
/*** Returns a stateful value, and a function to update it.** @version 16.8.0* @see https://reactjs.org/docs/hooks-reference.html#usestate*/

useContext会根据传入的上下文对象自动推导出context的类型，当然也可以使用泛型来设置context的类型，如下：

interface ITheme {
	color: string;
}
const ThemeContext = React.createContext<ITheme>({ color: "red" });

// 自动推导出类型为ITheme
const theme = useContext(ThemeContext); // 等同于const theme = useContext<ITheme>(ThemeContext);

useReducer

声明定义：

function useReducer<R extends Reducer<any, any>>(reducer: R,initialState: ReducerState<R>,initializer?: undefined
): [ReducerState<R>, Dispatch<ReducerAction<R>>];
/*** `useRef` returns a mutable ref object whose `.current` property is initialized to the passed argument* (`initialValue`). The returned object will persist for the full lifetime of the component.** Note that `useRef()` is useful for more than the `ref` attribute. It’s handy for keeping any mutable* value around similar to how you’d use instance fields in classes.** @version 16.8.0* @see https://reactjs.org/docs/hooks-reference.html#useref*/

上面只列出了一种类型定义，我在项目中也是使用这种定义去指定useReducer的类型。普通的案例如下：

type StateType = {name: string;age: number;
}

type Actions = {type: 'Change_Name';payload: string;
} | {type: 'Change_Age';payload: number;
}

const initialState = {name: '小明',age: 18
}

const reducerAction: Reducer<StateType, Actions> = ( state,action, ) => {switch (action.type) {case 'Change_Name':return { ...state, name: action.payload };case 'Change_Age':return { ...state, age: action.payload };default:return state;}
};

function Index() {const [state, dispatch] = useReducer(reducerAction, initialState);return (<div><div>姓名：{state.name}</div><div>年龄：{state.age}</div></div>);
}

可以看到，这样能够得到正确的类型推断，但是略微繁琐。在这篇文章中，学到了一个泛型定义，可以稍微简化一下定义Actions的过程。案例如下：

// 定义一个生成Action类型的泛型
type ActionMap<M extends Record<string, any>> = {[Key in keyof M]: M[Key] extends undefined? {type: Key}: {type: Keypayload: M[Key]}
}

type StateType = {name: string;age: number;
}

// 定义具体的Action类型
type PayloadType = {Change_Name: string;Change_Age: number;
}

/** ActionMap<PayloadType>会生成类型{Change_Name: {type: Types.Name;payload: string;};Change_Age: {type: Types.Age;payload: number;};}而keyof ActionMap<PayloadType>则会生成 'Change_Name' | 'Change_Age'的类型。所以Action最终的类型便为：type Actions = {type: Types.Name;payload: string;} | {type: Types.Age;payload: number;}
*/
type Actions = ActionMap<PayloadType>[keyof ActionMap<PayloadType>]

const initialState = {name: '小明',age: 18
}

const reducerAction: Reducer<StateType, Actions> = ( state,action, ) => {switch (action.type) {case Types.Name:return { ...state, name: action.payload };case Types.Age:return { ...state, age: action.payload };default:return state;}
};

我们定义了一个ActionMap泛型，该泛型会将传入的类型{key: value}生成为新的{key: {type: key, payload: value }类型。然后我们利用keyof关键字获取到所有的key，就可以得到我们所需要的{type: key1, payload: value1} | {type: key2, payload: value2}的类型了。只要我们定义好PayloadType类型，则可以自动推导出我们需要的Actions类型。如果你觉得这样写还是很繁琐，那么可以去看我的这篇文章在TypeScript中使用useReducer，里面介绍了简化的useReducer使用方式。

useImperativeHandle

声明定义：

 function useImperativeHandle<T, R extends T>(ref: Ref<T>|undefined, init: () => R, deps?: DependencyList): void;// NOTE: this does not accept strings, but this will have to be fixed by removing strings from type Ref<T>/** * `useImperativeHandle` customizes the instance value that is exposed to parent components when using * `ref`. As always, imperative code using refs should be avoided in most cases. * * `useImperativeHandle` should be used with `React.forwardRef`. * * @version 16.8.0 * @see https://reactjs.org/docs/hooks-reference.html#useimperativehandle */

useImperativeHandle可以让自定义组件通过ref属性，将内部属性暴露给父组件进行访问。因为是函数式组件，所以需要结合forwardRef一起使用。案例如下：

interface FancyProps {}

interface FancyRef {focus: () => void;
}

const FancyInput = forwardRef<FancyRef, FancyProps>((props, ref) => {const inputRef = useRef<HTMLInputElement>(null);useImperativeHandle(ref, () => ({focus: () => {inputRef.current?.focus();}}));return (<input ref={inputRef} {...props} />);
})

const Parent = () => {// 定义子组件refconst inputRef = useRef<FancyRef>(null);return (<div><FancyInput ref={inputRef}/><button onClick={() => {// 调用子组件方法inputRef.current?.focus();}}>聚焦</button></div>)
}

Axios请求/响应定义封装

axios是很流行的http库，他的ts封装已经很完美了，我们只做简单的二次封装，返回通用的数据响应格式。首先在utils/request.ts中创建一个构造axios实例的生成器：

import axios, { AxiosInstance, AxiosRequestConfig, AxiosResponse } from 'axios';

// 拦截器定义
export interface RequestInterceptors {// 请求拦截requestInterceptors?: (config: AxiosRequestConfig) => AxiosRequestConfigrequestInterceptorsCatch?: (err: any) => any// 响应拦截responseInterceptors?: (config: AxiosResponse) => AxiosResponseresponseInterceptorsCatch?: (err: any) => any
}

// 生成axios实例的参数，实例可以单独传入拦截器
export interface RequestConfig extends AxiosRequestConfig {interceptorsObj?: RequestInterceptors
}

// loading请求数量
let loadingCount: number = 0;

// 打开loading
const showLoading = () => {loadingCount ++;if(loadingCount > 0) {// 显示loading// Loading.show()}
}

// 关闭loading
const hideLoading = () => {loadingCount --;if(loadingCount <= 0) {// 隐藏loading// Loading.hide();}
}

function RequestBuilder(config: RequestConfig) {const { interceptorsObj, ...res } = config;const instance: AxiosInstance = axios.create(res);// 全局请求拦截器instance.interceptors.request.use((request: AxiosRequestConfig) => {// 显示loadingshowLoading();console.log('全局请求拦截器');// TODO：全局的请求头操作等等return request;},(err: any) => err,)/** * 实例请求拦截器  * 要注意 axios请求拦截器为倒序执行，所以要将实例请求拦截器注册在全局请求拦截器后面 */instance.interceptors.request.use(interceptorsObj?.requestInterceptors,interceptorsObj?.requestInterceptorsCatch,)/** * 实例响应拦截器 * axios响应拦截器为正序执行，所以要将实例响应拦截器注册在全局响应拦截器前面 */instance.interceptors.response.use(interceptorsObj?.responseInterceptors,interceptorsObj?.responseInterceptorsCatch,)// 全局响应拦截器instance.interceptors.response.use((response: AxiosResponse) => {console.log('全局响应拦截器');// 关闭loadinghideLoading();// TODO: 通用的全局响应处理，token过期重定向登录等等// 返回值为res.data，即后端接口返回的数据，减少解构的层级，以及统一响应数据格式。return response.data},(err: any) => {// 关闭loadinghideLoading();// TODO: 错误提示等return err;},)return instance;
}

export const http = RequestBuilder({baseURL: '/api'});

该生成器可以实现每个实例有单独的拦截器处理逻辑，并且实现全局的loading加载效果，全局拦截器的具体实现可以根据项目实际需求进行填充。生成器已经完成，但是还没法定制我们的通用响应数据，接下来我们在typings.d.ts中重新定义axios模块：

import * as axios from 'axios';

declare module 'axios' {// 定制业务相关的网络请求响应格式， T 是具体的接口返回类型数据export interface CustomSuccessData<T> {code: number;msg?: string;message?: string;data: T;[keys: string]: any;}export interface AxiosInstance {// <T = any>(config: AxiosRequestConfig): Promise<CustomSuccessData<T>>;request<T = any, R = CustomSuccessData<T>, D = any>(config: AxiosRequestConfig<D>): Promise<R>;get<T = any, R = CustomSuccessData<T>, D = any>(url: string, config?: AxiosRequestConfig<D>): Promise<R>;delete<T = any, R = CustomSuccessData<T>, D = any>(url: string, config?: AxiosRequestConfig<D>): Promise<R>;head<T = any, R = CustomSuccessData<T>, D = any>(url: string, config?: AxiosRequestConfig<D>): Promise<R>;post<T = any, R = CustomSuccessData<T>, D = any>(url: string,data?: D,config?: AxiosRequestConfig<D>,): Promise<R>;put<T = any, R = CustomSuccessData<T>, D = any>(url: string,data?: D,config?: AxiosRequestConfig<D>,): Promise<R>;patch<T = any, R = CustomSuccessData<T>, D = any>(url: string,data?: D,config?: AxiosRequestConfig<D>,): Promise<R>;}
}

完成以上操作后，我们在业务代码中具体使用：

import { http } from '@/utils/request';

interface Req {userId: string;
}

interface Res {userName: string;userId: string;
}

// 获取用户信息接口
const getUserInfo = async (params: Req) => {return http.get<Res>('/getUserInfo', {params})
}

这个时候getUserInfo返回的就是CustomSuccessData<Res>类型的数据了。至此我们对axios简单的封装也就完成了。