如何在 ChartJS 中销毁折线图

Question

I got a graph that updates when I select start and end date from my JSON data. But the old graph still appears when I hover over the points.

I have read a lot of post about using myLineChart.destroy(); but I'm unable to find a means to add to my graph .

 var cdata = [{ "_id": "585b544f5c86b6c8537c34d6", "topic": "Humidity", "message": 30, "message1": 2, "when": "2016-12-22T04:19:27.000Z" }, { "_id": "585b54505c86b6c8537c34d7", "topic": "Humidity", "message": 10, "message1": 25, "when": "2016-12-22T04:19:28.000Z" }, { "_id": "585b54515c86b6c8537c34d8", "topic": "Humidity", "message": 20, "message1": 30, "when": "2016-12-22T04:19:29.000Z" }, { "_id": "585b54525c86b6c8537c34d9", "topic": "Humidity", "message": 50,"message1": 40, "when": "2016-12-22T04:19:30.000Z" }, { "_id": "585b54535c86b6c8537c34da", "topic": "Humidity", "message": 45, "message1": 21, "when": "2016-12-22T04:19:31.000Z" }] var labeldata = []; var chrtdata = []; var chartdata = []; for(var i =0; i < cdata.length; i++) { labeldata.push(cdata[i].when); chrtdata.push(cdata[i].message) chartdata.push(cdata[i].message1) } var ctx = document.getElementById("myChart").getContext("2d"); var myChart = new Chart(ctx, { type: 'line', data: { labels: labeldata, datasets: [{ label: 'Humidity', data: chrtdata, backgroundColor: "rgba(255, 51, 0,0.6)" }, { label: 'Temperature', data: chartdata, backgroundColor: "rgba(102, 0, 255,0.6)" }, ] } });

 <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.2.2/Chart.min.js"></script> <canvas id="myChart" width="400" height="400"></canvas>

I would appreciate if someone can help me out with this.

Answer 1

Here is the example you can change your graph with dynamic values without destroying it. Hope it helps.

function getRandomJson() {
    var cdata = [{
        "_id": "585b544f5c86b6c8537c34d6",
        "topic": "Humidity",
        "message": Math.floor(Math.random() * (100 - 20 + 1)) + 20,
        "message1": Math.floor(Math.random() * (50 - 5 + 1)) + 5,
        "when": "2016-12-22T04:19:27.000Z"
    }, {
        "_id": "585b54505c86b6c8537c34d7",
        "topic": "Humidity",
        "message": Math.floor(Math.random() * (80 - 1 + 1)) + 1,
        "message1": Math.floor(Math.random() * (40 - 5 + 1)) + 5,
        "when": "2016-12-22T04:19:28.000Z"
    }, {
        "_id": "585b54515c86b6c8537c34d8",
        "topic": "Humidity",
        "message": Math.floor(Math.random() * (90 - 20 + 1)) + 20,
        "message1": Math.floor(Math.random() * (60 - 20 + 1)) + 20,
        "when": "2016-12-22T04:19:29.000Z"
    }, {
        "_id": "585b54525c86b6c8537c34d9",
        "topic": "Humidity",
        "message": Math.floor(Math.random() * (50 - 40 + 1)) + 40,
        "message1": Math.floor(Math.random() * (70 - 30 + 1)) + 30,
        "when": "2016-12-22T04:19:30.000Z"
    }, {
        "_id": "585b54535c86b6c8537c34da",
        "topic": "Humidity",
        "message": Math.floor(Math.random() * (85 - 20 + 1)) + 20,
        "message1": Math.floor(Math.random() * (65 - 35 + 1)) + 35,
        "when": "2016-12-22T04:19:31.000Z"
    }];
    return cdata;
}

loadGraph();
function loadGraph() {
var labeldata = [];
var chrtdata = [];
var chartdata = [];
var cdata = getRandomJson();
for(var i =0; i < cdata.length; i++)
{
  labeldata.push(cdata[i].when);
  chrtdata.push(cdata[i].message)
  chartdata.push(cdata[i].message1)
}
var ctx = document.getElementById("myChart").getContext("2d");
var myChart = new Chart(ctx, {
  type: 'line',
  data: {
    labels: labeldata,
    datasets: [{
      label: 'Humidity',
      data: chrtdata,
      backgroundColor: "rgba(255, 51, 0,0.6)"
    },
    {
      label: 'Temperature',
      data: chartdata,
      backgroundColor: "rgba(102, 0, 255,0.6)"
    },
    ]
  }
});
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.2.2/Chart.min.js"></script>

<button type="button" onClick="loadGraph()">Change Me!</button>
<canvas id="myChart" width="400" height="400"></canvas>