关于前端:走进开源项目-urlcat-源码分析

在《走进开源我的项目 – urlcat》中，对我的项目整体进行了剖析，对如何做开源也有了进一步的理解，该篇再深入研究下 urlcat 源码。

该我的项目到底做了什么？

// 惯例写法一
const API_URL = 'https://api.example.com/';

function getUserPosts(id, blogId, limit, offset) {const requestUrl = `${API_URL}/users/${id}/blogs/${blogId}/posts?limit=${limit}&offset=${offset}`;
  // send HTTP request
}

// 惯例写法二
const API_URL = 'https://api.example.com/';

function getUserPosts(id, blogId, limit, offset) {const escapedId = encodeURIComponent(id);
  const escapedBlogId = encodeURIComponent(blogId);
  const path = `/users/${escapedId}/blogs/${escapedBlogId}`;
  const url = new URL(path, API_URL);
  url.search = new URLSearchParams({limit, offset});
  const requestUrl = url.href;
  // send HTTP request
}

// 应用 urlcat 之后的写法
const API_URL = 'https://api.example.com/';

function getUserPosts(id, limit, offset) {const requestUrl = urlcat(API_URL, '/users/:id/posts', { id, limit, offset});
  // send HTTP request
}

源码共 267 行，其中正文占了近 110，代码只有 157 行。正文跟代码靠近 1:1，接下来咱们逐段剖析。

import qs, {IStringifyOptions} from 'qs';

// eslint-disable-next-line @typescript-eslint/no-explicit-any
export type ParamMap = Record<string, any>;
export type UrlCatConfiguration =
  Partial<Pick<IStringifyOptions, 'arrayFormat'> & {objectFormat: Partial<Pick<IStringifyOptions, 'format'>>}>

该我的项目是在 qs 我的项目的根底上并应用 typescript 进行开发，其中定义了 2 个类型，有几个不太理解知识点 type、Recode、Partial 和 Pick。

相同点：都能够形容对象或者函数，且能够应用 extends 进行拓展

不同点：

type 能够申明根本类型别名，联结类型，和元组等类型，但 interface 不行

// 根本类型别名
type Name = string | number;

// 联结类型
interface Common {name: string;}
interface Person<T> extends Common {
  age: T;
  sex: string;
}

type People<T> = {
  age: T;
  sex: string;
} & Common;

type P1 = Person<number> | People<number>;

// 元组
type P2 = [Person<number>, People<number>];

跟 typeof 联合应用

const name = "小明";

type T= typeof name;

Reacord 是 TypeScript 的一种工具类。

// 惯例写法
interface Params {[name: string]: any;
}

// 高级写法
type Params = Recode<string, any>

将传入的属性变为可选项

interface DataModel {
  name: string
  age: number
  address: string
}

let store: DataModel = {
  name: '',
  age: 0,
  address: ''
}

function updateStore (
  store: DataModel,
  payload: Partial<DataModel>
):DataModel {
  return {
    ...store,
    ...payload
  }
}

store = updateStore(store, {
  name: 'lpp',
  age: 18
})

从类型 Type 中，筛选一组属性组成一个新的类型返回。这组属性由 Keys 限定，Keys 是字符串或者字符串并集。

interface Person {
  name: string
  age: number
  id: string
}

// 幼儿没有 id
type Toddler = Pick<Person, 'name' | 'age'>

/**
 * Builds a URL using the base template and specified parameters.
 *
 * @param {String} baseTemplate a URL template that contains zero or more :params
 * @param {Object} params an object with properties that correspond to the :params
 *   in the base template. Unused properties become query params.
 *
 * @returns {String} a URL with path params substituted and query params appended
 *
 * @example
 * ```ts
 * urlcat('http://api.example.com/users/:id', { id: 42, search: 'foo'})
 * // -> 'http://api.example.com/users/42?search=foo
 * ```
 */
export default function urlcat(baseTemplate: string, params: ParamMap): string;

/**
 * Concatenates the base URL and the path specified using '/' as a separator.
 * If a '/' occurs at the concatenation boundary in either parameter, it is removed.
 *
 * @param {String} baseUrl the first part of the URL
 * @param {String} path the second part of the URL
 *
 * @returns {String} the result of the concatenation
 *
 * @example
 * ```ts
 * urlcat('http://api.example.com/', '/users')
 * // -> 'http://api.example.com/users
 * ```
 */
export default function urlcat(baseUrl: string, path: string): string;

/**
 * Concatenates the base URL and the path specified using '/' as a separator.
 * If a '/' occurs at the concatenation boundary in either parameter, it is removed.
 * Substitutes path parameters with the properties of the @see params object and appends
 * unused properties in the path as query params.
 *
 * @param {String} baseUrl the first part of the URL
 * @param {String} path the second part of the URL
 * @param {Object} params Object with properties that correspond to the :params
 *   in the base template. Unused properties become query params.
 *
 * @returns {String} URL with path params substituted and query params appended
 *
 * @example
 * ```ts
 * urlcat('http://api.example.com/', '/users/:id', { id: 42, search: 'foo'})
 * // -> 'http://api.example.com/users/42?search=foo
 * ```
 */
export default function urlcat(
  baseUrl: string,
  pathTemplate: string,
  params: ParamMap
): string;

/**
 * Concatenates the base URL and the path specified using '/' as a separator.
 * If a '/' occurs at the concatenation boundary in either parameter, it is removed.
 * Substitutes path parameters with the properties of the @see params object and appends
 * unused properties in the path as query params.
 *
 * @param {String} baseUrl the first part of the URL
 * @param {String} path the second part of the URL
 * @param {Object} params Object with properties that correspond to the :params
 *   in the base template. Unused properties become query params.
 * @param {Object} config urlcat configuration object
 *
 * @returns {String} URL with path params substituted and query params appended
 *
 * @example
 * ```ts
 * urlcat('http://api.example.com/', '/users/:id', { id: 42, search: 'foo'}, {objectFormat: {format: 'RFC1738'}})
 * // -> 'http://api.example.com/users/42?search=foo
 * ```
 */
export default function urlcat(
  baseUrlOrTemplate: string,
  pathTemplateOrParams: string | ParamMap,
  maybeParams: ParamMap,
  config: UrlCatConfiguration
): string;

export default function urlcat(
  baseUrlOrTemplate: string,
  pathTemplateOrParams: string | ParamMap,
  maybeParams: ParamMap = {},
  config: UrlCatConfiguration = {}): string {if (typeof pathTemplateOrParams === 'string') {
    const baseUrl = baseUrlOrTemplate;
    const pathTemplate = pathTemplateOrParams;
    const params = maybeParams;
    return urlcatImpl(pathTemplate, params, baseUrl, config);
  } else {
    const baseTemplate = baseUrlOrTemplate;
    const params = pathTemplateOrParams;
    return urlcatImpl(baseTemplate, params, undefined, config);
  }
}

这部分代码是利用 TypeScript 定义重载函数类型，采纳间断多个重载申明 + 一个函数实现的形式来实现，其作用是为了保障在调用该函数时，函数的参数及返回值都要兼容所有的重载。

例如下图，第三个参数类型在重载函数类型中并不存在。

以下代码是外围，作者通过职责拆散的形式，将外围办法代码简化。

// 外围办法
function urlcatImpl(
  pathTemplate: string,
  params: ParamMap,
  baseUrl: string | undefined,
  config: UrlCatConfiguration
) {// 第一步 path('/users/:id/posts', { id: 1, limit: 30}) 返回 "/users/1/posts" 和 limit: 30
  const {renderedPath, remainingParams} = path(pathTemplate, params);
    // 第二步 移除 Null 或者 Undefined 属性
  const cleanParams = removeNullOrUndef(remainingParams);
    // 第三步 {limit: 30} 转 limit=30
  const renderedQuery = query(cleanParams, config);
    // 第四步 拼接返回 /users/1/posts?limit=30
  const pathAndQuery = join(renderedPath, '?', renderedQuery);

    // 第五步 当 baseUrl 存在时，执行残缺 url 拼接
  return baseUrl ? joinFullUrl(renderedPath, baseUrl, pathAndQuery) : pathAndQuery;
}

做开源并不一定要造个更好的轮子，但能够让这个轮子变得更好。通过该我的项目，也发现自己在 TypeScript 方面的有余，持续学习，再接再厉。

玩转 TypeScript 工具类型（上）
你不晓得的 TypeScript 高级类型
请别误用 TypeScript 重载函数类型

玩转 TypeScript 工具类型（中）
玩转 TypeScript 工具类型（下）

关于前端:走进开源项目-urlcat-源码分析

第一段

interface 与 type 的区别

Record 的用处

Partial 的用处

Pick 的用处

第二段

第三段

总结

参考文章

拓展浏览