data() {
  return {
    files: myFiles as FileList;
  }
}

data(): {
  files?: <FileList | null>;
} {
  return {
      files:  undefined,
  };
}

interface Data {
  files?: <FileList | null>;
}

export default Vue.extend<Data, Methods, Computed, Props>({
  data() {
      return {
        files: undefined
      };
   }
 });

interface someType {
  child: {
     [key: string]: string;
  }
}

interface someType {
  child: Record<string, string>
}