Typescript runtime error: cannot read property of undefined (enum)

I just found out the hard way that this can also happen if you have circular imports.

In Typescript there are 2 kinds of enums:

• Classic enum:

During TS to JS transpilation they are converted to real objects, so they exist at runtime.

enum Response {
    No = 0,
    Yes = 1,
}

const yes = Response.Yes; // Works at runtime

const nameOfYes = Response[yes]; // Also works at runtime because a reverse mapping is also generated during transpilation

• const enum (the one you are using):

Const enums are removed during transpilation in JS so you can not use them at runtime. As per TS doc const enums exists to avoid paying the cost of extra generated code and additional indirection when accessing enum values.

const enum Response {
    No = 0,
    Yes = 1,
}

const yes = Response.Yes; // At runtime: ReferenceError: Response is not defined

const nameOfYes = Response[yes]; // During transpilation: TS2476: A const enum member can only be accessed using a string literal.

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So just change your const enum to enum and your runtime error will be gone.