[Solved]-Ionic 3 + Angular 4 + chart.js - loading data from array-Chart.js

The problem here is you use an async method getTecajRazdoblje(). But you're trying to fill the array sync way. So you need to correct that. Try this:

 this.hnbProvider.getTecajRazdoblje(datum_poc, datum_kraj).subscribe(tecaj => 
     {
       this.tecaj = tecaj;
       var i = 0;
       for (var key in this.tecaj) {
       if (this.tecaj[key].valuta == this.o_valuta){
        this.array[i] = this.tecaj[key].srednji_tecaj;
        i++;
       }   

      this.lineChart = new Chart(this.lineCanvas.nativeElement, 
       {
             type: 'line',
             data: {
                 labels: this.lista_valuta,
                 datasets: [
                     {
                         label: "My First dataset",
                         fill: false,
                         lineTension: 0.1,
                         backgroundColor: "rgba(75,192,192,0.4)",
                         borderColor: "rgba(75,192,192,1)",
                         borderCapStyle: 'butt',
                         borderDash: [],
                         borderDashOffset: 0.0,
                         borderJoinStyle: 'miter',
                         pointBorderColor: "rgba(75,192,192,1)",
                         pointBackgroundColor: "#fff",
                         pointBorderWidth: 1,
                         pointHoverRadius: 5,
                         pointHoverBackgroundColor: "rgba(75,192,192,1)",
                         pointHoverBorderColor: "rgba(220,220,220,1)",
                         pointHoverBorderWidth: 2,
                         pointRadius: 1,
                         pointHitRadius: 10,
                         data:this.array,
                         spanGaps: false,
                     }
                 ]
             }
         });
       }
   });
  }