The type `Map<string, enum>` cannot be assigned to `{ [key: string]: enum }`. The indexing signature is not present in the type `Map<string, enum>`

Suppose we have the following:

export enum Relationship {}

export interface Invitee {}

export interface InviteesResponse {
    invitees: Invitee[];
    relationships: { [key: string]: Relationship }; // mapping userIds to relationships
}



async function getInvitees(userId: string): Promise<InviteesResponse> {
...
        const invitees: Invitee[] = [];
        const relationships: Map<string, Relationship> = new Map();
...
        // this line is where the error occurs with relationships
        return { invitees, relationships };

When I consulted Webstorm for a solution, it suggested the following change:

async function getInvitees(userId: string): Promise<{ invitees: Invitee[]; relationships: Map<string, Relationship> }> {

I am struggling to grasp the underlying issue. Why do I need to destructure the type before returning it?

Here's the error message once more:

Type 'Map<string, Relationship>' cannot be assigned to type '{ [key: string]: Relationship; }'.   An index signature is missing in type 'Map<string, Relationship>'.

Answer №1

The problem I encountered was quite straightforward. The syntax

relationships: { [key: string]: Relationship };
is not suitable for a map.

The correct format should be:

relationships: Map<string, Relationship>;

I mistakenly believed that maps did not require an explicit TypeScript type, but now I understand that they do, so everything is resolved!

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