1 简介

“Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification.”

**

  • Class不可以被修改，但可以被继承，添加新的属性和方法来扩展功能_ ```typescript abstract class FileWriter { write(content: string): number; }

// buffered for a large-size file class BufferedFileWriter extends FileWriter { write(content: string): number; write(buff: ArrayBuffer, off: number, len: number): number; skip(num: number): number; }

// able to rollback class RollbackFileWriter extends FileWriter { write(content: string): number; rollback(): boolean; }

  2. - Function接口不可以被修改，但可以添加扩展参数来扩展功能
  3. ```typescript
  4. // a.ts
  5. export interface Options {
  6.   op1: string;
  7.   op2: number;
  8. }
  9. export function format(num: number, options: Options): string {
  10.   // ...
  11. }
  13. // b.ts
  14. import type { Options } from 'a.ts';
  15. import { format } from 'b.ts';
  17. export interface Options {
  18.   op3: boolean;
  19. }
  20. export function format(num: number, options: Options): string {
  21.   // ...
  22. }

2 Example

  1. //  @yy/sl-tools
  2. const format = (value: number, platformName: platformNameTypes): string | null => {
  3.   const supportPlatforms = ['STOREFRONT', 'ADMIN', 'DASH'];
  4.   const hitPlatform = supportPlatforms.indexOf(platformName) === -1;
  5.   let baseFormatOptions;
  6.   if (window === undefined) {
  7.     return null;
  8.   }
  9.   if (hitPlatform) {
  10.     console.error('请传入第二个参数platformName，目前仅支持STOREFRONT、ADMIN、DASH');
  11.     return null;
  12.   }
  13.   if (platformName === 'STOREFRONT') {
  14.     baseFormatOptions = {
  15.       code: Cookies.get('currency_code'),
  16.       lang: Cookies.get('lang'), // 目前商家前台还没有该字段.. todo...
  17.     };
  18.   } else if (platformName === 'ADMIN') {
  19.     baseFormatOptions = {
  20.       code: Cookies.get('a_currency_code'),
  21.       lang: Cookies.get('a_lang'),
  22.     };
  23.   } else if (platformName === 'DASH') {
  24.     baseFormatOptions = {
  25.       code: Cookies.get('d_currency_code'), // 目前dash还没有该字段（预留）
  26.       lang: Cookies.get('d_lang'), // 目前dash还没有该字段（预留
  27.     };
  28.   }
  29.   return baseFormat(value, baseFormatOptions);
  30. };
  • 改变接口，不兼容旧版本：破坏client调用代码
    • 无法估计有多少Client
    • 海量回归测试
  • 耦合其他应用代码：貌离神合，仅仅是空间上的隔离
    • 应用修改影响公共包
    • 公共包修改影响应用
  • 耦合其他职责（读取Cookies）：违反SRP原则
    • 分离配置读取代码
    • 约定接口或协议，而不约定实现


3 改进

  • configManager.ts ```typescript export enum StorageType { Cookies = ‘cookies’, SessionStorage = ‘sessionStorage’, LocalStorage = ‘localStorage’, IndexedDB = ‘indexedDB’, }

interface BaseOptions { type: StorageType; }

export interface Config { lang: string; code: string; }

interface CookiesOptions extends BaseOptions { key: Record; }

interface SessionStorageOptions extends BaseOptions { // … }

type LocalStorageOptions = interace SessionStorageOptions;

interface IndexedDBOptions extends BaseOptions { // … }

export type ConfigOptions = CookiesOptions | SessionStorageOptions | LocalStorageOptions | IndexedDBOptions;

export function getConfig(options: ConfigOptions): Config { // …. }

  2. - `currency.ts`
  3. ```typescript
  4. import _ from 'lodash';
  5. import type { CookiesOptions } from './configManager';
  6. import { StorageType, getConfig } from './configManager'
  8. let DEFAULT_OPTIONS: ConfigOptions = {
  9.   type: StorageType.Cookies,
  10.   key: {
  11.     lang: 'lang',
  12.       code: 'currency_code',    
  13.     },
  14. };
  16. let options: ConfigOptions = DEFAULT_OPTIONS;
  18. export function setOptions(opts: ConfigOptions) {
  19.   // merge
  20.   options = _.merge({}, DEFAULT_OPTIONS, opts);
  21. }
  23. export function formatCurrency(number) {
  24.   // ...
  25.   const config = getConfig(options);
  26.   // ....
  27. }
  • 使用 ```typescript // 应用Admin初始化: app.ts

import { setOptions, StorageType } from ‘@yy/sl-tools’;

setOptions({ type: StorageType.Cookies, key: { lang: ‘a_lang’, code: ‘a_currency_code’ }, });

// 使用 import { formatCurrency } from ‘@yy/sl-tools’; formatCurrency(number); ```