CODEWITHSUNDEEP
typescriptnpm
naomi
naomi

Reputation: 2643

Error referring to enum imported from npm types

I recently added typings to a private npm module.

One of the module's exported type is the following enum:

export enum ServerResponseCode {
  LoginFailed: 'loginFailed',
  LoginExpired: 'loginExpired'
}

Then it is imported by another typescript project and used as following:

import { ServerResponseCode } from 'private-module'

if(response.code === ServerResponseCode.LoginExpired)

This code does not raise any compilation errors, but on runtime I get an error: 'Cannot read property LoginExpired of undefined'

Why is this happening and how could I fix it?

Upvotes: 5

Views: 1467

Answers (1)

naomi
naomi

Reputation: 2643

Solution is to simply export a const enum in the type declaration file of private-module:

export const enum ServerResponseCode {
  LoginFailed: 'loginFailed',
  LoginExpired: 'loginExpired'
}

Short explanation from this stackoverflow thread:

The enum is defined as const so that any reference to its elements are inlined (by ts compiler), this way avoid a run time lookup to the ServerResponseCode object which is actually undefined (because .d.ts files do not result in any JS).

Upvotes: 3

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