@injectable()
export class MyWidget extends ReactWidget {
    ...
    @inject(WorkspaceService)
    protected readonly workspaceService: WorkspaceService;
    @inject(MonacoWorkspace)
    protected readonly MonacoWorkspace: MonacoWorkspace;
    @postConstruct()
    protected async init(): Promise<void> {
        ...
        this.onWorkspaceSave();
    }
    onWorkspaceSave(): void {
        this.MonacoWorkspace.onWillSaveTextDocument(event => {
            this.saveSpreadsheet()
        });
    }
    saveSpreadsheet = () => {
        socket.emit('save', {});
    }