Flowtype

Question

我有一个来自 select 输入的字符串类型的值，但是我想将它传递给函数 (updateLanguage) argument 带有类型别名的字符串枚举 (Language)。

我面临的问题是 Flow 只允许我调用 updateLanguage 如果我明确地将我的字符串值与枚举字符串进行比较并且我想使用像这样的数组函数array.includes.

这是我的问题的代码简化：

// @flow

type SelectOption = {
    value: string
};
const selectedOption: SelectOption = {value: 'en'};

type Language = 'en' | 'pt' | 'es';
const availableLanguages: Language[] = ['en', 'pt'];

function updateLanguage(lang: Language) {
    // do nothing
}

// OK
if(selectedOption.value === 'en' || selectedOption.value === 'pt') {
  updateLanguage(selectedOption.value);
}

// FLOWTYPE ERRORS
if(availableLanguages.includes(selectedOption.value)) {
  updateLanguage(selectedOption.value);
}

运行流 v0.30.0 给出以下输出：

example.js:21
 21: if(availableLanguages.includes(selectedOption.value)) {
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ call of method `includes`
 21: if(availableLanguages.includes(selectedOption.value)) {
                                    ^^^^^^^^^^^^^^^^^^^^ string. This type is incompatible with
  9: const availableLanguages: Language[] = ['en', 'pt'];
                               ^^^^^^^^ string enum

example.js:22
 22:   updateLanguage(selectedOption.value);
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function call
 22:   updateLanguage(selectedOption.value);
                      ^^^^^^^^^^^^^^^^^^^^ string. This type is incompatible with
 11: function updateLanguage(lang: Language) {
                                   ^^^^^^^^ string enum


Found 2 errors

如何以可扩展的方式检查字符串值是否是枚举的一部分？

Answer 1

这是一个可扩展且安全的解决方案：

const languages = {
  en: 'en',
  pt: 'pt',
  es: 'es'
};

type Language = $Keys<typeof languages>;

const languageMap: { [key: string]: ?Language } = languages;

function updateLanguage(lang: Language) {
    // do nothing
}

type SelectOption = {
    value: string
};
const selectedOption: SelectOption = {value: 'en'};

if(languageMap[selectedOption.value]) {
  updateLanguage(languageMap[selectedOption.value]);
}

Flowtype - 字符串与字符串枚举不兼容

Flowtype - string incompatible with string enum

javascript

string

enums

typechecking