目录

• 项目目录及ts文件划分
• 在项目中使用TypeScript具体实践
• 组件声明
• React Hooks使用
• useState
• useRef
• useCallback
• useMemo
• useContext
• useReducer
• useImperativeHandle
• Axios请求/响应定义封装

前言：

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.ReactElement
  const url: string
  export 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

• 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>
  );
}

• 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。

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: Key
        payload: 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。

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ref
  const 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) => AxiosRequestConfig
  requestInterceptorsCatch?: (err: any) => any
  // 响应拦截
  responseInterceptors?: (config: AxiosResponse) => AxiosResponse
  responseInterceptorsCatch?: (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loading
      showLoading();
      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loading
      hideLoading();
      // 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loading
      hideLoading();
      // 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。