Property '<properyName>' of exported interface has or is using private name '<name>'

Question

I declare an interface:

export interface ApiClientMetodOptions {
    initialFilterSatement?: string;
    fieldsMapping?: {
        [K in keyof P]?: string;
    };
    requestParams?: IRequestParams<P>;
    additionalParams?: {
        [key: string]: unknown;
    };
    additionalHeaders?: {
        [key: string]: string;
    };
    cancelOption?: IRequestCancelOption;
}

but get following error: Property 'fieldsMapping' of exported interface has or is using private name 'P'. I done this for encapsulate the type and using it in some methods. For example:

export interface IApiClient {
    /**
     * Generic function for fetching a list of a certain instances
     * @param fieldsMapping function converting fields of `P`-type object to a query field names
*/
getEntities<P, T>(
    url: string,
    options: {
        instanceToEntity?: (instance: unknown) => T;
    } & ApiClientMetodOptions,
): Promise<T[]>;

I don't know "typescript" very deeply. What I'm doing wrong and how to fix this problem?

Answer 1

You need to add the generic parameter P to your interface definition like this:

export interface ApiClientMetodOptions<P> {
    initialFilterSatement?: string;
    fieldsMapping?: {
        [K in keyof P]?: string;
    };
    requestParams?: IRequestParams<P>;
    additionalParams?: {
        [key: string]: unknown;
    };
    additionalHeaders?: {
        [key: string]: string;
    };
    cancelOption?: IRequestCancelOption;
}

And then in your method defintion add the parameter as well:

export interface IApiClient {
    /**
     * Generic function for fetching a list of a certain instances
     * @param fieldsMapping function converting fields of `P`-type object to a query field names
*/
getEntities<P, T>(
    url: string,
    options: {
        instanceToEntity?: (instance: unknown) => T;
    } & ApiClientMetodOptions<P>,
): Promise<T[]>;