Discovering Typescript: Inferring the type of a union containing specific strings

I am working with a specific type called IPermissionAction which includes options like 'update', 'delete', 'create', and 'read'.

type IPermissionAction = 'update' | 'delete' | 'create' | 'read'

When trying to create an object that conforms to this type, such as:

const object =  {
                  subject: 'correspondence',
                  action: 'update' as keyof IPermissionAction
                }

I encountered an error message stating:

Argument of type 'string | number | unique symbol' is not assignable to parameter of type 'IPermissionAction'.
  Type 'string' is not assignable to type 'IPermissionAction'.ts(2345)

I attempted to use keyof but it didn't resolve the issue.

typescript

Answer №1

A recommended approach to achieve this task is as follows:

type IPermissionAction = 'edit' | 'remove' | 'add' | 'view';

type CustomType = {
    name: string,
    operation: IPermissionAction
}

const item: CustomType = {
    name: 'notes',
    operation: 'edit'
}

Answer №2

To restrict object.action as type IPermissionAction, you can utilize this type assertion without the need for an additional type for object. Simply eliminate the keyof operator.

type IPermissionAction = "update" | "delete" | "create" | "read";

const object = {
  subject: "correspondence",
  action: "update" as IPermissionAction
};

object.action = "";
// ~~~~~~~~~~ Type '""' is not assignable to type 'IPermissionAction'.

Try it on TypeScript Playground

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