Learn how to define an array of member names in TypeScript for a specific type

Is there a way to generate an array containing the names of members of a specific type in an expression?

For example:

export type FileInfo  = {
    id: number
    title ?: string
    ext?: string|null
}
const fileinfo_fields = ["id","ext","title"];

I need to provide these field names as arguments to different methods for various types.

For instance:

const info = await api.get_info<FileInfo>(1234, fileinfo_fields);

This is necessary because managing multiple types with numerous fields can be error-prone.

Although type information is not accessible at runtime, I simply require a constant array that includes the member names.

Something along the lines of this, but I'm struggling to figure it out:

const fileinfo_fields = magic_extract_expression<FileInfo>; // ????

Do you know if achieving this is feasible in any way?

Answer №1

The terms "field names" within objects are referred to as keys. Each object contains a collection of "key-value" pairs. TypeScript allows you to access the keys of a certain type using the keyof operator.

For instance:

type FileInfo = {
    id: number
    title?: string
    ext?: string|null
}

let key: keyof FileInfo; // "id" | "title" | "ext";

If you need an array of keys, you can achieve it by doing the following:

const keys: (keyof FileInfo)[] = ["id", "title", "ext"];

To learn more about the keyof operator, check out the documentation in the TypeScript handbook.

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