Using data from API with Chart JS

Question

I am getting data from an api and then reformatting part of it into an array using .map(), I am successfully able to do this, but when it comes time to pass it into Chart JS as data it does work. I am able to pass in a normal, hard coded, array but not my own data...

I tried using an Angular directive (NG2-Charts) to help out thinking maybe that was the problem, but that doesn't work either...

Component.ts: ... Other variable and stuff up here...

getStockData() {
    this.stocksService.getStockData()
      .subscribe(
        (response) => {
          for(var i = 0; i < response.length; i++) {
            this.stockOpen.push(response[i]['open']);
          }
          console.log('after loop: ', this.stockOpen);
        },
        (error) => console.error(error)
      );
      console.log('real: ', this.stockOpen);
      console.log('test: ', this.testData);
  }

  // Chart JS version
  buildStockChart() {
    var ctx = document.querySelector("#chart");
    this.chart = new Chart(ctx, {
      type: 'bar',
      data: {
        labels: [1,2,3,4,5],
        datasets: [
          { 
            data: this.stockOpen,
            borderColor: "#3cba9f",
            fill: false
          }
        ]
      },
      options: {
        legend: {
          display: false
        },
        scales: {
          xAxes: [{
            display: true
          }],
          yAxes: [{
            display: true
          }],
        }
      }
    });
  }

  // NG2-Charts version
  public lineChartData:Array<any> = [
    {data: this.testData},
  ];
  public lineChartLabels:Array<any> = ['January', 'February', 'March', 'April', 'May', 'June', 'July'];
  public lineChartOptions:any = {
    responsive: true
  };

Result from console.log():

Have you tried logging after the for loop (inside of the subscribe closure)? — Hodrobond
– Hodrobond, Commented Jul 24, 2018 at 23:05
@Hodrobond I just tried it and updated the post. It is different but I'm still not totally sure what the issue is — Garrett
– Garrett, Commented Jul 24, 2018 at 23:09
In the first set of console.logs, the 'real' was empty because it wasn't populated yet. Now it looks like you have populated data, and I'm not sure what else is wrong. My guess would be you're trying to use stockOpen before it gets set. When do you call buildStockChart in relation to getStockData, and can you ensure it waits to build until you've gotten your data? — Hodrobond
– Hodrobond, Commented Jul 24, 2018 at 23:16

Joseph Agbing · Accepted Answer · 2018-07-25 00:06:33Z

3

i also have same problem with chart JS on angular so i force to use another chart. im now using angular 2 chart js.

i think the problem here is the delay of data fetch by API, the CHART component is already render on html view but the data is still not fetch by the API service.

try to add this code on your code block. This will handle the data if API service data is available. ()=>{this.buildStockChart();}

 this.stocksService.getStockData()
      .subscribe(
        (response) => {
          for(var i = 0; i < response.length; i++) {
            this.stockOpen.push(response[i]['open']);
          }
          console.log('after loop: ', this.stockOpen);
        },
        ()=>{
        this.buildStockChart();
        }
      );
      console.log('real: ', this.stockOpen);
      console.log('test: ', this.testData);
  }

This chart is easy to manage for dynamic instances.

Hope this chart will work on you.

https://www.npmjs.com/package/angular2-chartjs

edited Jul 25, 2018 at 0:06

answered Jul 24, 2018 at 23:48

Joseph Agbing

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1 Comment

M.Laida Over a year ago

@Joseph Agbing WOw amazing!

Bruno · Accepted Answer · 2018-07-24 23:35:44Z

0

When are you calling the buildStockChart() method?

You should call it right after the for loop into the callback you pass to the subscribe method, since that's the moment when this.stockOpen is populated (before that moment it will be empty as you are seeing in the console).

answered Jul 24, 2018 at 23:35

Bruno

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1 Comment

Garrett Over a year ago

Yeah this worked. Still getting used to lifecycle hooks, thanks.

Pipo · Accepted Answer · 2018-12-22 19:49:12Z

As @Joseph Agbing, I was unable to get it work with angular 7. I'm now using chart.js only

npm install chart.js --save

with into my `someChart.component.html`

<div style="display: block"> <canvas id="canvas">{{chart}}</canvas> </div>

into my `someChart.component.ts`

called from my httpClient.post(...).subscribe(lData => (setChartDataFromEntities(lDataProcessed), ...)

import { Chart } from 'chart.js';

export class someClass {

/**
* 
* @param aDate 
* @param aChargeUnitArray 
*/
setChartDataFromEntities( aDate: Date, aChargeUnitArray: ChargeUnit[] ){
    console.debug('setChartDataFromEntities->', aChargeUnitArray)
    let lChartDataArray = []
    let lChartDataLineDataArray: Array<Number> = []
    let lChartLabelsArray: string[] = []
    let l_s: string
    aChargeUnitArray.forEach(element => {
        lChartDataLineDataArray.push(element.charge)
        lChartLabelsArray.push(MiscHelper.dateTimeHMSForChart(element.timestamp))
    });
    lChartDataArray.push(
        {
            data: lChartDataLineDataArray,
            label: MiscHelper.dateForGui(aDate),
        }
    )

    this.chart = new Chart('canvas', {
    type: 'line',
    data: {
        labels: lChartLabelsArray,
        datasets: lChartDataArray
    },
    options: {
        legend: {
            display: false
        },
        scales: {
        xAxes: [{
            display: true
        }],
        yAxes: [{
            display: true
        }],
        }
    }
    });    

    this.statusMessage = 'Chart loaded'
}

hope it helps somebody more than the day I wasted trying to get it work...

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Using data from API with Chart JS

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with into my `someChart.component.html`

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