How to use Chart.js in Angular4?

Question

I'm stuck trying to use Chart.js in Angular4. I'm using Visual Studio.

I tried to use ViewChild but then I decided to try the official way:
https://www.chartjs.org/docs/latest/getting-started/usage.html

package.json:

"@angular/core": "4.2.5",
"@types/chart.js": "^2.7.40",
"chart.js": "^2.7.3",

my-chart.html:

<canvas id="myChart" width="400" height="400"></canvas>
or
<canvas #chartCanvas [style.width]="width" [style.height]="height"></canvas>

"my-chart.ts:

import { Chart } from "chart.js"

export class SalesChart implements OnInit {

    @Input("chartWidth") width: string = "10%"
    @Input("chartHeight") height: string = "20%"
    @ViewChild("chartCanvas") private chartCanvas:any


// when click the button:
drawChart() {
    // new Chart does not accep HTMLElement
    // var ctx = document.getElementById("myChart")   

    var myChart = new Chart("myChart", {
        type: 'bar',
        data: {
            labels: ["Red", "Blue"],
            datasets: [{
                label: '# of Votes',
                data: [12, 19, 3, 5, 2, 3],
                backgroundColor: [
                    'rgba(255, 99, 132, 0.2)',
                    'rgba(54, 162, 235, 0.2)',
                ],
                borderColor: [
                    'rgba(255,99,132,1)',
                    'rgba(54, 162, 235, 1)'
                ],
                borderWidth: 1
            }]
        },
        options: {
            scales: {
                yAxes: [{
                    ticks: {
                        beginAtZero: true
                    }
                }]
            }
        }
    })  
}

The canvas is initially rendered with the assigned dimensions but when the drawChart() is executed the canvas is set with width and height = "0" and it become empty.
Initial HTML element:

<canvas _ngcontent-c2="" height="400" id="myChart" width="400"></canvas>

Resulting HTML element:

<canvas _ngcontent-c2="" height="0" id="myChart" width="0" class="chartjs-render-monitor" style="display: block; height: 0px; width: 0px;"></canvas>

I can change the with/height but the canvas is absolutely empty.

I also tried using the ViewChild solution but when I pass something valid to Chart() I have the same result: width and height set to "0" and empty canvas.

        //var ctx = (<HTMLCanvasElement>this.chartCanvas.nativeElement).getContext("2d")
    var ctx = document.getElementById("chartCanvas") as HTMLCanvasElement

I found some tutorials that use:

chart = []
// and this in the HTML template
<canvas ...>{{ chart }}</canvas>

With this approach when I have no errors the chart result to be [Object Object].

Someone have any idea why the chart is not created?

Khalid · Accepted Answer · 2018-11-24 20:06:55Z

2

I usually use chart.js through primeng, and even if I don't want to use primeng, I follow their example, because I find it clean. You can see how they implement it here: https://github.com/primefaces/primeng/blob/master/src/app/components/chart/chart.ts

answered Nov 24, 2018 at 20:06

Khalid

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2 Comments

Alex 75 Over a year ago

I used their example but is practically like mine with extra properties configuration. Their package.json has chart.js 2.7.3, like me, but Angular 7.. I saw many examples in Angular 5 but I think the problem exists with Angular 4. The resulting canvas maintain the size but remains empty.

Alex 75 Over a year ago

I made some other small changes and it works! Thanks.

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