Chart.js Update

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.5.0/Chart.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<canvas id="forecast" width="300" height="150"></canvas>
<button id="0" type="button" >Dataset 1</button>
<button id="1" type="button" >Dataset 2</button>

JavaScript

var chart_labels = ['06:00', '09:00', '12:00', '15:00', '18:00', '21:00'];
var temp_dataset = ['1', '8', '10', '10', '9', '7'];
var rain_dataset = ['0', '0', '6', '32', '7', '2'];

var ctx = document.getElementById("forecast").getContext('2d');
  
var config = {
	type: 'bar',
  data: {
    labels: chart_labels,
    datasets: [
      {
        type: 'line',
        label: "Temperature (Celsius)",
        yAxisID: "y-axis-0",
        fill: false,
        data: temp_dataset,
      },
      {
        type: 'bar',
        label: "Precipitation (%)",
        yAxisID: "y-axis-1",
        data: rain_dataset,
      }]
  },
  options: {
    scales: {
      yAxes: [{
        position: "left",
        "id": "y-axis-0",
      }, {
        position: "right",
        "id": "y-axis-1",
      }]
    }
  }
};

var forecast_chart = new Chart(ctx, config);

$("#1").click(function (){
  var chart_labels = ['00:00', '03:00', '06:00', '09:00', '12:00', '15:00', '18:00', '21:00'];
  var temp_dataset = ['5', '3', '4', '8', '10', '11', '10', '9'];
  var rain_dataset = ['0', '0', '1', '4', '19', '19', '7', '2'];
	forecast_chart.update();
});