Draw horizontal line on chart in chart.js on v2

Question

I have drawn a line chart using chart.js. For the labels and datasets i am getting values from the database. I am new to chart.js and its very powerful library, yet i am una

Answer 1

if you want to draw threshold line,easiest way is that using mixed line chart.

Note: Make an array filled with threshold value and the length should be same as your dataset.

var datasets = [1, 2, 3];
var ctx = document.getElementById('chart').getContext('2d');
var thresholdValue = 2;
var thresholdHighArray = new Array(datasets.length).fill(thresholdValue);
var myChart = new Chart(ctx, {
            type: 'line',
            data: {
                labels: [],
                datasets: [
                {datasets}, thresholdHighArray]
            },         
            options: {
                responsive: true,
                legend: {
                    position: 'bottom',
                },
                scales: {
                    xAxes: [{
                        display: true,
                        scaleLabel: {
                                display: true,
                                labelString: 'Readings'
                        }
                    }],
                    yAxes: [{
                        display: true,
                        scaleLabel: {
                                display: true,
                                labelString: 'Reading ( °C )'
                        }
                    }]
                },
                annotation: {
                  annotations: [
                    {
                      type: "line",
                      mode: "vertical",
                      scaleID: "x-axis-0",
                      borderColor: "red",
                      label: {
                        content: "",
                        enabled: true,
                        position: "top"
                      }
                    }
                  ]
                }
        });
    };