I have an array with acceptable mime types:
export const frontend = {
...
zipMimeTypes: [
"application/zip",
"application/x-zip-compressed",
"multipart/x-zip",
],
} as const;
I want to include it in another file and use it like so:
frontend.zipMimeTypes.includes(file.type)
However, my TS compiler is complaining about file.type
Argument of type 'string' is not assignable to parameter of type '"application/zip" | "application/x-zip-compressed" | "multipart/x-zip"'.
I just do:
[
"application/zip",
"application/x-zip-compressed",
"multipart/x-zip",
].includes(file.type)
It works
The issue is in as const. Instead, you can define an interface to use with frontend:
interface Frontend {
zipMimeTypes: string[];
}
const frontend: Frontend = {
zipMimeTypes: [
"application/zip",
"application/x-zip-compressed",
"multipart/x-zip"
]
};
Although forcing zipMimeTypes to be a string array will get rid of the error, you have now lost your typing for zipMimeTypes.
Instead I would create a type for your zipMimeTypes.
The advantages is that code-completion works nicely too.
export const frontend = {
zipMimeTypes: [
"application/zip",
"application/x-zip-compressed",
"multipart/x-zip",
],
} as const;
type zipMimeType = typeof frontend.zipMimeTypes[number];
interface File {
type: zipMimeType;
}
const file:File = {
type: 'application/zip'
}
if (frontend.zipMimeTypes.includes(file.type)) {
//etc.
}