Flot graph with line hover

HTML

<script src="http://people.iola.dk/olau/flot/jquery.flot.js"></script>
<div id="placeholder" style="width:600px;height:300px;"></div>

CSS

body {
    font-family: sans-serif;
    font-size: 16px;
    margin: 50px;
    max-width: 800px;
}
#flotTip {
}

JavaScript

//Tooltip plugin
(function ($) {
    var options = {
        tooltip: false,
        //boolean
        tooltipOpts: {
            content: "%s | X: %x | Y: %y.2",
            //%s -> series label, %x -> X value, %y -> Y value, %x.2 -> precision of X value
            dateFormat: "%y-%0m-%0d",
            shifts: {
                x: 10,
                y: 20
            },
            defaultTheme: true
        }
    };

    function init(plot) {

        var tipPosition = {
            x: 0,
            y: 0
        };
        var opts = plot.getOptions();

        function updateTooltipPosition(pos) {
            tipPosition.x = pos.x;
            tipPosition.y = pos.y;
        };

        function onMouseMove(e) {

            var pos = {
                x: 0,
                y: 0
            };
            pos.x = e.pageX;
            pos.y = e.pageY;

            updateTooltipPosition(pos);
        };

        function timestampToDate(tmst) {

            var theDate = new Date(tmst);

            return $.plot.formatDate(theDate, opts.tooltipOpts.dateFormat);
        };

        plot.hooks.bindEvents.push(function (plot, eventHolder) {

            var to = opts.tooltipOpts;
            var placeholder = plot.getPlaceholder();
            var $tip;

            if (opts.tooltip === false) return;

            if ($('#flotTip').length > 0) {
                $tip = $('#flotTip');
            } else {
                $tip = $('<div />').attr('id', 'flotTip');
                $tip.appendTo('body').hide().css({
                    position: 'absolute'
                });

                if (to.defaultTheme) {
                    $tip.css({
                        'background': 'rgba(41, 41, 41, 0.9)',
                            'z-index': '4000',
                            'padding': '0',
                            'border-radius': '0.5em',
                            'font-size': '0.8em',
                            'border': 'none'
                    });
...