How create array based on typescript types, whitout use enum type [duplicate]

Question

I have a UserRoles type in typscript

type = 'student' | 'editor' | 'moderator' | 'admin'
or
type UserRoles = 'student' | 'editor' | 'moderator' | 'admin'

how can I create an array based on these types? something like

const roles = Array.from(UserRoles)

Thanks in advance :)

var userRoles:UserRoles[] = []; // would create an empty array of UserRoles — Rick
– Rick, Commented Jun 28, 2020 at 17:21

subashMahapatra · Accepted Answer · 2020-06-28 17:11:30Z

3

UserRoles only refers to a type, you can not use it as a value. But you can explictly create a readonly array for the roles and extract the type from it. For example,

const roles = ['student', 'editor', 'moderator', 'admin'] as const;

// type will be  'student' | 'editor' | 'moderator' | 'admin'
type UserRoles = typeof roles[number]

let uRole: UserRoles;
// valid
uRole = 'student';

// compile-time error
uRole = 'hello'

typescript playground

answered Jun 28, 2020 at 17:11

subashMahapatra

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3 Comments

Yung Silva Over a year ago

after setting user Roles to type enum, I can't use it as I used before .. https://image.prntscr.com/image/dS2lBofuSWG0PfW9w4YS6A.png

subashMahapatra Over a year ago

enums and union types are two different things. If you want to modify your code base you can fix the error by assigning the role value like this role: Roles.student. If you don't want to modify your code base use the solution that i have provided, it will not break any existing code.

subashMahapatra Over a year ago

Here is another example ts playground

Cristian Sarghe · Accepted Answer · 2020-06-28 17:16:20Z

0

One good practice in your case is using Enums. Besides numbers, you can also have string enums (which is what you need).

enum UserRoles {
    Student = 'student',
    Editor = 'editor',
    Moderator = 'moderator',
    Admin = 'admin'
}

If you do it this way, you can consider the Enum an object and get an array of its values with

const values = Object.values(UserRoles);

answered Jun 28, 2020 at 17:16

Cristian Sarghe

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2 Comments

Yung Silva Over a year ago

after setting user Roles to type enum, I can't use it as I used before .. https://image.prntscr.com/image/dS2lBofuSWG0PfW9w4YS6A.png

Cristian Sarghe Over a year ago

@YungSilva This is something requested, but I doubt it has been implemented (github.com/microsoft/TypeScript/issues/17690). The common usage of enums is assigning Type.Value to the variable instead of a string literal. In your case, given the screenshots, you could do { ... ; role: Roles.student; ... }. Notice that you need to export the enum if you want to use it in a different file.

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