[英]Cannot define string enum typescript as string is not assignable
enum Cat {
cat1 = 'cat1',
cat2 = 'cat2',
cat3 = 'cat3',
cat4 = 'cat4',
cat5 = 'cat5'
}
const category: Cat = 'cat' + cat
Why do I get a typescript error for that?为什么我会收到 typescript 错误?
cat
is a number, so category
is a string. cat
是一个数字,所以category
是一个字符串。 But I want to define some specific string values for this variable.但我想为这个变量定义一些特定的字符串值。
Type 'string' is not assignable to type 'Cat'.
I assume you want category to be one of Cat, not the enum itself.我假设您希望类别成为 Cat 之一,而不是枚举本身。 so
所以
const cat = 4;
const category = Cat[`cat${cat}`] // category: Cat.cat4
This also gives you type safety if trying to access a number out of range.如果尝试访问超出范围的数字,这也可以为您提供类型安全。 playground
操场
enum Cat {
cat1 = 'cat1',
cat2 = 'cat2',
cat3 = 'cat3',
cat4 = 'cat4',
cat5 = 'cat5'
}
const cat = 4;
const category = Cat[`cat${cat}`]
const cat6 = 6;
const category6 = Cat[`cat${cat6}`] // Property 'cat6' does not exist on type 'typeof Cat'.
Typescript cant ensure that cat
is 1,2,3,4, or 5
since it could also be someThingElse
. Typescript 不能确保
cat
是1,2,3,4, or 5
因为它也可能是someThingElse
。 Therefore you have to tell typescript that you are sure its gonna be of type Cat
因此,您必须告诉 typescript 您确定它是
Cat
类型
The issue here is that the compiler wont allow 'cat' + someVar
to be used as type Cat
.这里的问题是编译器不允许将
'cat' + someVar
用作类型Cat
。
Please be cautious when using this, since you essentially overwrite the compilers error.使用它时请小心,因为您实际上会覆盖编译器错误。 You really need to make sure that whatever you're doing before will always be a valid cat.
您确实需要确保您之前所做的任何事情都将永远是一只有效的猫。
enum Cat {
cat1 = 'cat1',
cat2 = 'cat2',
cat3 = 'cat3',
cat4 = 'cat4',
cat5 = 'cat5',
}
const category: Cat = (('cat' + cat) as Cat);
enum Cat {
cat1 = 'cat1',
cat2 = 'cat2',
cat3 = 'cat3',
cat4 = 'cat4',
cat5 = 'cat5',
}
// this would be of however [Cat.cat1, Cat.cat2 ...] would be a lot safer.
// I would generally suggest not tot use dynamic enum values like this.
for (const i of [1,2,3,4,5]) {
const category: Cat = (('cat' + i) as Cat);
}
// the compiler would allow this as well, since you ensure that you know the type is going to be if type Cat
for (const i of ['dog']) {
const category: Cat = (('cat' + i) as Cat);
}
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