Iterating through array in Chart.js data field

Question

Update:

var voltagedata1 = [];
    batterybank1.forEach(function(element){
        var voltage = {x: element.timestamp, y:element.voltage};
        voltagedata1.push(voltage);
})

data: voltagedata1

I have an array which I want to iterate through in the data field of the Chart.js chart.

This code works for example:

data: [
    {x: '2019-08-12 09:40:15', y:4}, {x: '2019-08-13 09:40:15', y:5}, {x: '2019-08-14 09:40:15', y:6},
],

Then trying to iterate through the array as follows:

batterybank1.forEach(function(element){
    console.log(element)
    "{x:\'element.timestamp', y:element.voltage},"
})

The console.log(element) gives a correct output, however the chart is not getting updated... on the console I am getting no warnings/errors - just the graph does not output.

The following does not work either, only the console.log is outputted but the graph is not updated.

batterybank1.forEach(function(element){
    console.log(element)
    "{x:\'2019-08-12 09:40:15', 1},"
})

@MattEllen, the data field accepts data in the format as {x: , y: }, {x: , y: }, ... as far as I know - so I was trying to output that using the for loop in the data field. Refer to the first code part where I gave an example that works. — Luke Galea
– Luke Galea, Commented Aug 12, 2019 at 10:38
OK. Putting a string there will not output it to the console, or return it from a function. It will do nothing. How do you add data to a chart with chart.js? — Matt Ellen
– Matt Ellen, Commented Aug 12, 2019 at 10:45
I do not want that string to output to the console. Refer to my first example to see how data is added to chart.js - which is what I wanted to replicate then in the for loop — Luke Galea
– Luke Galea, Commented Aug 12, 2019 at 10:48

Matt Ellen · Accepted Answer · 2019-08-12 11:46:16Z

It's explained in the documentation, that you add your points to the chart one at a time, like so:

batterybank1.forEach(function(element){
       chart.data.datasets[0].data.push(element);
})

This is assuming that element is in the same format as the points in data.

After that you need to call chart.update(); to show the new data.

below is a working example:

let data = [{t: '2019-08-12 09:40:15', y:4}, {t: '2019-08-13 09:40:15', y:5}, {t: '2019-08-14 09:40:15', y:6}, {t: '2019-08-15 09:40:15', y:7}];

var chart = new Chart(document.getElementById('cht'), { type:'bar', data:
{
  datasets:[{
	label: 'CHRT - Chart.js Corporation',
	backgroundColor: '#ff0000',
  borderColor: '#ff0000',
  type: 'bar',
	pointRadius: 0,
	fill: false,
	lineTension: 0,
	borderWidth: 2,
  data: data}]
}, options:{
        scales: {
            xAxes: [
            {
              type: 'time',
						  distribution: 'series',
						  ticks: 
              {
							  source: 'data',
							  autoSkip: true
						  }
            }]
        }
    } });
    
document.getElementById('addPoints').addEventListener('click', function() {
      let extra = [{t: '2019-08-16 09:40:15', y:4}, {t: '2019-08-17 09:40:15', y:5}, {t: '2019-08-18 09:40:15', y:6}, {t: '2019-08-19 09:40:15', y:7}];
      extra.forEach(p =>
      {
        chart.data.datasets[0].data.push(p);
      });
      
      chart.update();
		});

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.8.0/Chart.min.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.8.0/Chart.bundle.js"></script>

<button id="addPoints">Add Points</button>

<canvas id="cht" class="chartjs" width="770" height="385" style="display: block; width: 770px; height: 385px;">

Thank you for that! I adopted a similar method - check update in original post.

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Iterating through array in Chart.js data field

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