我有一个来自选择输入的字符串类型的值,但我想将其传递到一个函数(updateLanguage(中,该函数接收一个具有类型别名的字符串枚举作为参数(Language(。
我面临的问题是,如果我明确地将字符串值与枚举字符串进行比较,并且我想使用array.includes这样的数组函数,Flow只允许我调用updateLanguage。
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
如何以可伸缩的方式检查字符串值是否是枚举的一部分?
这里有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]);
}