如何检查字符串是否为类型 [英] How to check if string in type

问题描述

我有类型:

export type PermissionType = 'creator' | 'editor' | 'viewer' 

在运行时，如何检查变量 userInput 是否实际上是上述类型之一

At run time, how to check if a variable userInput is actually one the type above

let userInput = 'foo' //
isOfTypePermission(userInput)  // should return false or throw an error

let userInput2 = 'creator'
isOfTypePermission(userInput2) // should return true

换句话说，如何将 PermissionType 类型编译成 javascript 数组，以便我可以执行 indexOf(userInput) > -1

In other word, how to get the type PermissionType compiled into a javascript array so that I can just do indexOf(userInput) > -1

推荐答案

不要过度复杂化.

function isOfTypePermission (userInput: string): userInput is PermissionType {
  return ['creator', 'editor', 'viewer'].includes(userInput);
}

参见打字稿中的`is`关键字有什么作用? 了解我们为什么不只使用 boolean 返回类型的更多信息.

See What does the `is` keyword do in typescript? for more information on why we don't just use a boolean return type.

如果您的 PermissionType 真的很长，那么从 const 值推断类型可能是值得的.

If your PermissionType is really long, then it might be worth it to infer the type from a const value instead.

const permissions = ['creator', 'editor', 'viewer'] as const;
type PermissionType = (typeof permissions)[number];

function isOfTypePermission (userInput: string): userInput is PermissionType {
  return (permissions as readonly string[]).includes(userInput);
}

甚至可能是一个 Set

const permissions = new Set(['creator', 'editor', 'viewer'] as const);
type PermissionType = typeof permissions extends Set<infer T> ? T : never;

function isOfTypePermission (userInput: string): userInput is PermissionType {
  return (permissions as Set<string>).has(userInput);
}

这篇关于如何检查字符串是否为类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！