export class DocProps { _createdAt: string | null = null; _updatedAt: string | null = null; _customProperties: { [name: string]: string } = {}; createdAt(date: string) { this._createdAt = date; return this; } updatedAt(date: string) { this._updatedAt = date; return this; } customProperty(name: string, item: string) { this._customProperties[name] = item; return this; } }