JSFiddle - React, Tailwind, and code Playground

HTML

<html>
 <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>sync test</title>

    <!--[if lte IE 8]><script language="javascript" type="text/javascript" src="../excanvas.min.js"></script><![endif]-->
    <script language="javascript" type="text/javascript" src="jquery-1.7.1.min.js"></script>
    <script language="javascript" type="text/javascript" src="http://yourjavascript.com/3245481321/flotr2-min.js"></script>

 </head>
    <body>
    <h1>Sync Test</h1>

    <div id="placeholder" style="width:600px;height:300px"></div>
    <div id="placeholder2" style="width:300px;height:200px"></div>

    <p>crosshair sync test.</p>
    </body>
</html>

JavaScript

var plot;
 var plot2;
 
 $(function () {
     var sin = [], cos = [];
     for (var i = 0; i < 14; i += 0.1) {
         sin.push([i, Math.sin(i)]);
         cos.push([i, Math.cos(i)]);
     }
 
     var data = [ { data: sin, label: "sin(x) = -0.00"},
                  { data: cos, label: "cos(x) = -0.00" } ];
 
     var options = {
                   series: { lines: { show: true } },
                   crosshair: { mode: "x"},
                   grid: { hoverable: true, autoHighlight: false },
                   yaxis: { min: -1.2, max: 1.2 },
                   mouse: { track: true }
             };
 
     plot = Flotr.draw(document.getElementById("placeholder"),data,options);
     plot2 = Flotr.draw(document.getElementById("placeholder2"),data, options);
     
     var plotDivs = ['placeholder', 'placeholder2'];
     var plotObjs = [plot, plot2];
     
     var updateAllCrosshairs = function(originalEvt, position, plotObj){
       
       for(var i = 0; i < plotObjs.length; i++){
     
         if(plotObj !== plotObjs[i]){
               updatePlotCrosshair(plotObjs[i], position);
         }
       }
     };
     
var updatePlotCrosshair = function(plotObj, pos){
      plotObj.crosshair.clearCrosshair();
      plotObj.crosshair.drawCrosshair(pos);
}; 
     
     for(var i = 0; i < plotDivs.length; i++){
       Flotr.EventAdapter.observe(document.getElementById(plotDivs[i]), 'flotr:mousemove', updateAllCrosshairs);
     }
 });