How do I get the numeric value from my enum with a instance from the enum?

Question

I am trying to get the number values of the enum IOSSubscriptionStatus but when I try to cast my string to the enum and then use that enum to get the number value I get the followin error

Type 'string' is not assignable to type 'number'.

Here is the code. I put a comment behind the line that throws the error

enum IOSSubscriptionStatus {
    'CANCEL' = 3,
    'DID_CHANGE_RENEWAL_PREF' = -1,
    'DID_CHANGE_RENEWAL_STATUS' = -1,
    'DID_FAIL_TO_RENEW' = 6, 
    'DID_RECOVER' = 1,
    'DID_RENEW' = 2,
    'INITIAL_BUY' = 4,
    'INTERACTIVE_RENEWAL' = 2,
    'PRICE_INCREASE_CONSENT' = 8,
    'REFUND' = 13,
    'RENEWAL' = 2,
}

export const handleAppStoreServerNotification = functions.region('europe-west1').https.onRequest(async (req, res) => {
  
    if (req.query.key !== developerNotificationKeys.key || req.body?.data == null)
        return res.status(200).send('Recieved successfully');

    const json = JSON.parse(req.body.data);
    const notificationType = json['notification_type'] as unknown as IOSSubscriptionStatus;

    if(notificationType === null || notificationType === undefined)
        return res.status(200).send('Recieved successfully');

    const notificationTypeId : number = IOSSubscriptionStatus[notificationType]; // This line throws the error
    
    return res.status(200).send('Recieved successfully');
});

But when I test it in TSPlayground

enum Test2 {
    "Yo" = 4,
    "Do" = 4,
    "Mo" = 2
}

const x :string = "Mo" ;

const test = x as unknown as Test2;
const conv : number = Test2[test]

console.log(conv);

I get the expected output of 2 as expected so why don't I get a value of type number in my cloud functions? I am running the code in a cloud function with typescript 3.8.0

Answer 1

Why do You think that 2 is unexpected ? Please take a look how TS will convert your code to JS: Before - TS version

enum Test2 {
    "Yo" = 4,
    "Do" = 4,
    "Mo" = 2
}

const x :string = "Mo" ;

const test = x as unknown as Test2;
const conv : number = Test2[test]

console.log(conv);

After, JS version

"use strict";
var Test2;
(function (Test2) {
    Test2[Test2["Yo"] = 4] = "Yo";
    Test2[Test2["Do"] = 4] = "Do";
    Test2[Test2["Mo"] = 2] = "Mo";
})(Test2 || (Test2 = {}));
const x = "Mo";
const test = x;
const conv = Test2[test];
console.log(conv);

So, Test2 is simple object

var Test2 = {2: "Mo", 4: "Do", Yo: 4, Do: 4, Mo: 2};
const x = "Mo";

const test = x;
const conv = Test2[test];// same as Test2["Mo"]