I am learning Typescript with React and i am having type compatibility issues while converting date.

Here is my data.ts file:

import { Result } from "./columns";

export enum Quality {
  High = "high",
  Medium = "medium",
  Low = "low",
}

// // The numbering represents the order the events are expected to occur,
// // First is the baseline, then the follow-up, and finally the conclusion.
// // All event's may not be present, but when they are, the earlier event will always be present.
export enum Event {
  Baseline = "Baseline",
  FollowUp = "FollowUp",
  Conclusion = "Conclusion",
}

// please do not edit the data, unless to add further examples
export const data: Result[] = [
  {
    patientId: "87gd2",
    scannedAt: new Date("2021-08-03T12:00:00Z"),
    score: 0.81,
    event: Event.FollowUp,
    sampleQuality: Quality.Low,
    dateOfBirth: "1990-01-01",
  },
  {
    patientId: "87gd2",
    scannedAt: new Date("2021-08-01T12:00:00Z"),
    score: 0.92,
    event: Event.Baseline,
    sampleQuality: Quality.High,
    dateOfBirth: "1990-01-01",
  },
  {
    patientId: "87gd2",
    scannedAt: new Date("2021-08-08T12:00:00Z"),
    score: 0.43,
    event: Event.Conclusion,
    sampleQuality: Quality.Low,
    dateOfBirth: "1990-01-01",
  },
  {
    patientId: "js27h",
    scannedAt: new Date("2021-08-02T12:00:00Z"),
    score: 0.74,
    event: Event.Baseline,
    sampleQuality: Quality.Medium,
    dateOfBirth: "1993-02-12",
  },
  {
    patientId: "9782e",
    scannedAt: new Date("2021-08-03T12:00:00Z"),
    score: 0.25,
    event: Event.Baseline,
    sampleQuality: Quality.Medium,
    dateOfBirth: "1981-04-12",
  },
  {
    patientId: "9782e",
    scannedAt: new Date("2021-08-21T12:00:00Z"),
    score: 0.21,
    event: Event.FollowUp,
    sampleQuality: Quality.High,
    dateOfBirth: "1981-04-12",
  },
];

And here are my interfaces

export interface Result {
  patientId: string; // the client specific identifier
  scannedAt: Date; // the time at which the sample was digitally scanned
  score: number; // the score of the sample
  event: Event; // the event that the sample was taken at
  sampleQuality: Quality; // the quality of the sample
  dateOfBirth: string; // the date of birth of the patient
}

export interface FormattedResult extends Result {
  formattedScannedAt: string;
  formattedDateOfBirth: string;
}

And here is my data formatter function:

export const formattedData: FormattedResult[] = data.map((item) => ({
  ...item,
  sampleQuality: formatQuality(item.sampleQuality),
  scannedAt: item.scannedAt.toLocaleString("en-US", {
    year: "numeric",
    month: "long",
    day: "numeric",
  }),
  score: item.score.toFixed(2),
  dateOfBirth: new Date(item.dateOfBirth).toLocaleDateString("en-US", {
    year: "numeric",
    month: "long",
    day: "numeric",
  }),
}));

In this formatter function it is giving the error like :

Type ‘{ sampleQuality: QualityValue; scannedAt: string; score: string; dateOfBirth: string; patientId: string; event: Event; }[]’ is not assignable to type ‘FormattedResult[]’.
Type ‘{ sampleQuality: QualityValue; scannedAt: string; score: string; dateOfBirth: string; patientId: string; event: Event; }’ is missing the following properties from type ‘FormattedResult’: formattedScannedAt, formattedDateOfBirth

I want to know what is wrong i am doing here.