chart.js로는 스크롤을 해도 y축이 보이게 하는 기능을 제공해주진 않지만 임의로 비슷하게 만들 수 있다. 

바로 canvas의 drawImage를 이용하는 방법이다. (물론 약간의 css기술도 필요하다)

아래의 코드처럼 animation이 끝났을 때 canvas의 drawImage를 이용하여 y축을 복사하면 된다.

<style type="text/css">
.chartWrapper {
  position: relative;
  top:15%;
}

.chartWrapper > canvas {
  position: absolute;
  left: 0;
  top: 0;
  pointer-events: none;
}

.chartAreaWrapper {
  overflow-x: scroll;
}
.chartAreaWrapper2 {
  width: 10000px;
}

</style>


<script src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.8.0.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.1.4/Chart.bundle.min.js"></script>
<script type="text/javascript" charset="utf-8" src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.1/Chart.min.js"></script>
<script type="text/javascript">
   var chartData = {
        labels: ["label1", "label2", "label3", "label4", "label5", "label6", "label7", "label8", "label9", "label10", "label11", "label12", "label13", "label14", "label15", "label16"],
        datasets: [{
            type: 'line',
            label: 'line',
            borderColor: "#FF6384",
            borderWidth: 2,
            fill: false,
            lineTension: 0,
            data: [
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10,
                Math.random()*10
            ]
        }, {
            type: 'bar',
            label: 'bar',
            backgroundColor: "#36A2EB",
            data: [
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000,
                Math.random()*25000
            ],
            borderColor: 'white',
            borderWidth: 2
        },]

    };
	
   $.fn.hasScrollBar = function() {
	    return (this.prop("scrollHeight") == 0 && this.prop("clientHeight") == 0)
	            || (this.prop("scrollHeight") > this.prop("clientHeight"));
   };

    window.onload = function() {
		var ctx9 = $('#chart9').get(0).getContext("2d");
		var ctx9Axis = $('#chart9Axis').get(0).getContext("2d");
		var ctx9Axis2 = $('#chart9Axis2').get(0).getContext("2d");
		
		changeChartLength(chartData);
		
		window.theChart9 = new Chart(ctx9, {
            type: 'bar',
            data: chartData,
            options: {
                responsive: true,
                scales: {
                	xAxes: [{
                		barThickness:50,
               		    gridLines: {
               		      display: false
               		    },
                        offset:true
                    }],
                    yAxes: [{
                        id: 'em',
                        type: 'linear',
                        poition: 'left',
                        ticks: {
	                        max: 25000,
	                        min: 0,
	                        stepSize: 5000
                        },
                        gridLines: {
                		    drawBorder: false//축과 데이터의 경계선 표시 여부
                		  }
                      }, {
                        id: 'ppm',
                        type: 'linear',
                        position: 'right',
                        ticks: {
                          max: 10,
                          min: 0,
	                      stepSize: 2
                        },
                        gridLines: {
                		    drawBorder: false//축과 데이터의 경계선 표시 여부
                		  }
                      }]
                },
                animation: {
    	            onComplete: function (animation) {
    	            	var sourceCanvas = ctx9.canvas;
    	            	var copyWidth = this.scales["em"].width;
    	            	var copyWidth2 = this.scales["ppm"].width;
    	            	var copyHeight = this.chart.height;
    	            	var targetElementWidth = ctx9.canvas.clientWidth;
    	                var targetElementHeight = ctx9.canvas.clientHeight;
    	                
    	            	ctx9Axis.canvas.width = copyWidth;
    	            	ctx9Axis.canvas.height = copyHeight;
    	            	
    	            	ctx9Axis.drawImage(sourceCanvas, 0, 0, targetElementWidth, targetElementHeight);

    	            	ctx9Axis2.canvas.height = copyHeight;
    	            	
    	            	var tmp = $("body").hasScrollBar() ? 16 : 0;
                        ctx9Axis2.canvas.width = targetElementWidth > window.innerWidth-tmp ? window.innerWidth-tmp : targetElementWidth;
                        ctx9Axis2.drawImage(sourceCanvas, 
                              				sourceCanvas.width - copyWidth2-15, 
                            				0, 
                            				copyWidth2+15, 
                            				sourceCanvas.height, 
                            				ctx9Axis2.canvas.width - copyWidth2 - 13.5 + (sourceCanvas.height - ctx9Axis2.canvas.height)/15, 
                            				0, 
                            				copyWidth2 + 13.5 - (sourceCanvas.height - ctx9Axis2.canvas.height)/15, 
                            				copyHeight);
    	            }
                }
            }
    });
</script>
<div class="chartWrapper">
	<div class="chartAreaWrapper">
		<div class="chartAreaWrapper2">
			<canvas id="chart9">
		</div>
	</div>

	<canvas id="chart9Axis" height="300" width="32">
	<canvas id="chart9Axis2" height="300" width="32">
</div>

ctx9Axis는 왼쪽 y축을 위한 canvas context이고

ctx9Axis2는 오른쪽 y축을 위한 canvas context이므로 필요한 대로 가져다가 쓰시면 된다.

참고 출처 : https://stackoverflow.com/questions/47038946/chartjs-v2-on-retina-display-has-label-size-issue-text-is-too-large