添加链接 注册    登录
link管理
链接快照平台
  • 输入网页链接，自动生成快照
  • 标签化管理网页链接
相关文章推荐
心软的香菜  ·  DTS Bundle Generator 使用教程·  1 月前    · 
痴情的铁板烧  ·  前端開發環境 + React + TS - ...·  1 月前    · 
开朗的硬盘  ·  R 快速合併多個檔案_以CSV為例 - ...·  2 周前    · 
安静的感冒药  ·  Best XML Parser Online·  1 月前    · 
低调的炒饭  ·  验证码_哔哩哔哩·  3 月前    · 
高兴的太阳  ·  历史的苦涩：建设三门峡水库的诸多失误(图)_ ...·  4 月前    · 
文质彬彬的香槟  ·  针对 SAML 设置用户身份验证类型 - ...·  2 年前    · 
link管理  ›  TypeScript 'instanceof' interface is it possible? - DEV Community
role typescript
https://dev.to/worldpwn/typescript-instanceof-interface-is-it-possible-5flk
帅气的钥匙扣
2 年前

I really like the power of interfaces in TypeScript and its duck typing. But what really bothers me is that I cannot check whether is something an instance of interface.

For example, we have decided to build a role model for the user class. User class will have different roles and based on role type it either has permissions or not. And we decided to describe roles as interfaces.

So I want to have code like this: 

class User {
    constructor(readonly role: IReader | IWriter){};
interface IReader  {
interface IWriter {
    readonly permissions: Array<string>
function guardAccess(user: User){
    // Oh no it is not working 😱
    // Error TS2693
    if (user.role instanceof IReader){
      throw new AccessDeniedException();
function guardAccess(user: User){
    // ✔️ no error
    if (user.role.name === "reader"){
      throw new AccessDeniedException();
    Enter fullscreen mode
    Exit fullscreen mode

// lets create a user with role reader
const user = getUser();
if (user.role.name === "reader"){
    user.role.name;
    user.role.permissions; // 🛑 error
else if (user.role.name === 'writer'){
    user.role.name;
    user.role.permissions; // ✔️ no error
    Enter fullscreen mode
    Exit fullscreen mode

if (user.role.name === "editor"){
 // 🛑 Error: TS 2367This condition will always return 'false'
 // since the types '"reader" | "writer"' and '"editor"' 
 // have no overlap.
    Enter fullscreen mode
    Exit fullscreen mode

That is it. Now we can have similar behavior to the instance of the interface in TypeScript. 


Thank you for reading!

function guardAccess(user: User) {
  if (!user.permissions.includes(Permission.canWrite)) {
    throw new AccessDeniedException();
    Enter fullscreen mode
    Exit fullscreen mode
          
This article is not about specific domain but about how to check interface at runtime. 


And proposed solution works if you don’t need polymorphism. 

For example you have role reader that can only read and role writer with claims for what it can write. 

    Once unpublished, all posts by worldpwn will become hidden and only accessible to themselves.
    If worldpwn is not suspended, they can still re-publish their posts from their dashboard.
 
推荐文章
心软的香菜  ·  DTS Bundle Generator 使用教程
1 月前
痴情的铁板烧  ·  前端開發環境 + React + TS - iT 邦幫忙::一起幫忙解決難題，拯救 IT 人的一天
1 月前
开朗的硬盘  ·  R 快速合併多個檔案_以CSV為例 - HackMD
2 周前
安静的感冒药  ·  Best XML Parser Online
1 月前
低调的炒饭  ·  验证码_哔哩哔哩
3 月前
高兴的太阳  ·  历史的苦涩：建设三门峡水库的诸多失误(图)_资讯_凤凰网
4 月前
文质彬彬的香槟  ·  针对 SAML 设置用户身份验证类型 - Tableau
2 年前
Link管理   ·   Sov5搜索   ·   小百科
link管理 - 链接快照平台