Validate if JSON matches type

Question

I am getting some serialized information into my angular application on form if JSON. I would like to check if event property name is one of my preDefined strings.

Event name type:

EventName =
  'appInfo' |
  'connectivity' |
  'location' |
  'pushNotification' |
  'newVersion';

const foo: EventName = 'appInfo';
const bar: EventName = 'appInfos'; // error
const baz: EventName = JSON.parse('appInfos'); // no error
    
// validation
const nameValid = [
  'appInfo', 
  'connectivity', 
  'location', 
  'pushNotification', 
  'newVersion'
].includes(baz) // works, but I would need to change things here and in type if something changes

Answer 1

If you only want to maintain your strings in one place, you could put them in an array as const , then derive a typeof from the array.

const EVENT_NAMES = [
  'appInfo',
  'connectivity',
  'location',
  'pushNotification',
  'newVersion',
] as const;

type EventName = typeof EVENT_NAMES[number];

const foo: EventName = 'appInfo';
const bar: EventName = 'appInfos'; // error
const baz: EventName = JSON.parse('appInfos'); // no error

EVENT_NAMES.includes(baz);

EventName type will be:

const EVENT_NAMES: readonly ["appInfo", "connectivity", "location", "pushNotification", "newVersion"]

Answer 2

Based on answer from @bherbruck I changed EventName from type to enum. So my enum looks like

enum EventName {
  AppInfo = 'appInfo',
  Connectivity = 'connectivity',
  Location = 'location',
  PushNotification = 'pushNotification',
  NewVersion = 'newVersion'
}

and validation is

... && Object.values(EventName).includes(this.name);