Error: Unable to assign void to parameter type

Encountering TypeScript Error:

Argument type (response: Response<DSBMannschaftDTO[]>) => void is not
  assignable to parameter type ((value:Response<DSBMannschaftDTO[]>) =>
  (PromiseLike<void> | void)) null | undefined | undefined

Schema Overview:

export class DsbMannschaftDTO implements DataTransferObject {   
    id: number;   
    vereinId: number;   
    nummer: number;   
    benutzerId: number;   
    veranstaltungsId: number;   
    version: number;

    static copyFrom(optional: {
        id?: number,
        vereinId?: number,
        nummer?: number,
        benutzerId?: number;
        veranstaltungsId: number;
        version?: number  
    } = {}): DsbMannschaftDTO {
        const copy = new DsbMannschaftDTO();
        copy.id = optional.id || null;
        copy.vereinId = optional.vereinId || null;
        copy.benutzerId = optional.benutzerId || null;
        copy.veranstaltungsId = optional.veranstaltungsId || null;
        copy.nummer = optional.nummer || null;
        copy.version = optional.version || null;

        return copy;
    }
}

Code Implementation:

private loadTableRows() {
    this.loading = true;

    this.dsbMannschaftDataProvider.findAll()
        .then(onfulfilled:(response: Response<DsbMannschaftDTO[]>) => this.handleLoadTableRowsSuccess(response))
        .catch(onrejected:(response: Response<DsbMannschaftDTO[]>) => this.handleLoadTableRowsFailure(response));
}

Clarification on the Error Message, any insights appreciated. Thank you in advance!

Answer №1

The issue at hand lies within the definition of your object. The DsbMannschaftDTO is defined as follows:

id: number; <- value must be a number
vereinId: number;   <- value must be a number

However, when passing the options object with the following definition:

id?: number, <- can be a number or undefined
vereinId?: number, <- can be a number or undefined

This leads to the first inconsistency where number | undefined cannot be assigned to number.

Furthermore, you have written:

copy.id = optional.id || null; <- now copy.id can be a number, undefined, or null.

This introduces the second discrepancy where number | undefined | null is not compatible with number.

To resolve this, consider replacing null with 0 (or any appropriate default type) for better compatibility.

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