之前有人问过类似的问题，并收到了很多回复，我可能听起来重复了某些人的问题，但我只是迫切需要第三只眼睛。我在 angular 中的订阅函数中为变量分配一个值，但在订阅函数之外调用时，变量返回“未定义”。这就是我正在做的事情：

this.invoiceService.buildDataForDiscountGraph(this.usrId, this.currentYear)
      .subscribe( response => {
        this.discountsGraphData += response;
        //this.discountGraphData is of type 'string'
    });

This.discountsGraphData

在订阅函数中调用时返回所需的值，但在订阅函数之外，在另一个函数中，甚至我的模板中，它都是一个空字符串。

这是 buildDataForDiscountGraph() 函数的外观：

buildDataForDiscountGraph(u,y){
    return this.getUserInvoices(u)
      .pipe(
        map(response  => {
          if(Object.keys(response).length > 0)
          {
            let jan = 0, feb = 0, mar = 0, apr = 0;
            let may = 0, june = 0, july = 0, aug = 0;
            let sep = 0, oct = 0, nov = 0, dec = 0;

            for(let x = 0; x < Object.keys(response).length; x++) {
              let dateSplit = response[x]['datecreated'].split('-');
              let year = dateSplit[0];
              let month = dateSplit[1];

              if(y == year){
                if(month == '01')jan += response[x]['discount'];
                if(month == '02')feb += response[x]['discount'];
                if(month == '03')mar += response[x]['discount'];
                if(month == '04')apr += response[x]['discount'];
                if(month == '05')may += response[x]['discount'];
                if(month == '06')june += response[x]['discount'];
                if(month == '07')july += response[x]['discount'];
                if(month == '08')aug += response[x]['discount'];
                if(month == '09')sep += response[x]['discount'];
                if(month == '10')oct += response[x]['discount'];
                if(month == '11')nov += response[x]['discount'];
                if(month == '12')dec += response[x]['discount'];
              }
            }

            return [
              jan, feb, mar, apr, may, june, july, aug,
              sep, oct, nov, dec
            ].join();
          }  
      })
    )
  }

我不得不将代码移到我的服务中，试图找出导致它的原因。服务函数 getUserInvoices() 调用一个端点，如下所示；

/**
   * Get Invoices
   *
   * @param userId
   * @param Limit
   * @param Offset
   */
  getUserInvoices(usrId, limit?, offset?){
    return this.http.get(this.apiEndPoint + usrId + '/invoices?limit=' + limit + '&offset=' + offset)
      .pipe(
        map( data =>
          {
            return (data ? data : []);
          }
        )
      )
  }