Chartjs-Retrieve value returned from a function in Angular

Do you have a full working example?

My guess would be to initialize doughnutChartData inside the subscribe:

online: number;
doughnutChartData;

onlineNumber() : number {
  this.memberService.onlineUsers().subscribe((number: number) => {
    this.online = number;
    doughnutChartData = [this.online, 9];
  });
  return this.online;
}

Updated answer: add another method to initializeDoughnutChartData and use it inside userNumber and onlineNumber:

initializeDoughnutChartData() {
    if (this.online != undefined && this.term != undefined) {
        this.doughnutChartData = [this.online, this.term];
    }
}

Call this method inside userNumber and onlineNumber:

onlineNumber() : number {
    this.memberService.onlineUsers().subscribe((number: number) => {
      this.online = number;
      this.initializeDoughnutChartData();
    })
    return this.online;
}

userNumber() {
    this.memberService.userNumber().subscribe((number: number) => {
      this.term = number;
      this.initializeDoughnutChartData();
    })
}