在《走進開源專案 - urlcat》中，對專案整體進行了分析，對如何做開源也有了進一步的瞭解，該篇再深入研究下 urlcat 原始碼。
該專案到底做了什麼？
// 常規寫法一
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=${offset}`;
// send HTTP request
}
// 常規寫法二
const API_URL = 'https://api.example.com/';
function getUserPosts(id, blogId, limit, offset) {
const escapedId = encodeURIComponent(id);
const escapedBlogId = encodeURIComponent(blogId);
const path = `/users/${escapedId}/blogs/${escapedBlogId}`;
const url = new URL(path, API_URL);
url.search = new URLSearchParams({ limit, offset });
const requestUrl = url.href;
// send HTTP request
}
// 使用 urlcat 之後的寫法
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
}原始碼共 267 行，其中註釋佔了近 110，程式碼只有 157 行。註釋跟程式碼接近 1:1 ，接下來我們逐段分析。
第一段
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'>> }>該專案是在 qs 專案的基礎上並使用 typescript 進行開發，其中定義了 2 個型別，有幾個不太瞭解知識點 type 、 Recode 、Partial 和 Pick 。
interface 與 type 的區別
- 相同點：都可以描述物件或者函式，且可以使用
extends進行擴充 不同點：
type 可以宣告基本型別別名，聯合型別，和元組等型別，但 interface 不行
// 基本型別別名 type Name = string | number; // 聯合型別 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>; // 元組 type P2 = [Person<number>, People<number>];跟 typeof 結合使用
const name = "小明"; type T= typeof name;
Record 的用途
Reacord 是 TypeScript 的一種工具類。
// 常規寫法
interface Params {
[name: string]: any;
}
// 高階寫法
type Params = Recode<string, any>Partial 的用途
將傳入的屬性變為可選項
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
})Pick 的用途
從型別 Type 中，挑選一組屬性組成一個新的型別返回。這組屬性由 Keys 限定， Keys 是字串或者字串並集。
interface Person {
name: string
age: number
id: string
}
// 幼兒沒有id
type Toddler = Pick<Person, 'name' | 'age'>第二段
/**
* 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);
}
}這部分程式碼是利用 TypeScript 定義過載函式型別，採用連續多個過載宣告 + 一個函式實現的方式來實現，其作用是為了保證在呼叫該函式時，函式的引數及返回值都要相容所有的過載。
例如下圖，第三個引數型別在過載函式型別中並不存在。
第三段
以下程式碼是核心，作者通過職責分離的方式，將核心方法程式碼簡化。
// 核心方法
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 屬性
const cleanParams = removeNullOrUndef(remainingParams);
// 第三步 {limit: 30} 轉 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 當 baseUrl 存在時，執行完整 url 拼接
return baseUrl ? joinFullUrl(renderedPath, baseUrl, pathAndQuery) : pathAndQuery;
}總結
做開源並不一定要造個更好的輪子，但可以讓這個輪子變得更好。通過該專案，也發現自己在 TypeScript 方面的不足，繼續學習，再接再厲。