styling SVG markers

<!doctype html>
<html>
<head>
  <meta charset="utf-8">
  <title>Styling SVG Markers</title>
  <style id="styles">
    html {
      background: hsl(0, 0%, 0%);
      -webkit-background-size: cover;
         -moz-background-size: cover;
              background-size: cover;
    }
    .wrap {
      max-width: 860px;
      margin: auto;
      overflow: auto;
    }
    .svg-container {
      width: 420px;
      padding: 15px;
      float: left;
    }
    .color-path {
      fill: none;
      stroke-width: 2.5px;
    }
    .layout-path {
      fill: none;
      stroke: none;
    }
    .marker {
      stroke: none;
    }
    .btn-light {
      cursor: pointer;
      fill: url(#btn-light);
      stroke: hsl(0, 0%, 60%);
      stroke-width: .5px;
    }
    .btn-light-txt {
      font-family: "Lucida Grande", "Lucida Sans Unicode", Helvetica, Arial, Verdana, sans-serif;
      text-anchor: middle;
      fill: hsl(0, 0%, 30%);
      stroke: none;
      font-size: 1rem;
      -webkit-user-select: none;
      pointer-events: none;
    }
    .splainin {
      font-family: "Lucida Grande", "Lucida Sans Unicode", Helvetica, Arial, Verdana, sans-serif;
      background : white;
      border-radius: 4px;
      color: hsl(0, 0%, 30%);
      float: left;
      font-size: .85rem;
      width: 380px;
      padding: 10px 12px;
      margin: 40px auto;
    }
    .splainin a {
      color: hsl(203, 100%, 50%);
      text-decoration: none;
      font-weight: 600;
    }
    .splainin ul {
      margin: 0;
      padding-left: 8px;
      list-style: none;
    }
    .pi {
      color: hsl(332, 98%, 51%);
    }
    @media only screen
      and (max-width : 870px) {
        .svg-container {
          float: none;
          display: block;
          margin: auto;
        }
        .splainin {
          float: none;
          display: block;
        }
    }

</style>
</head>
<body>
<div class="wrap">
<div class="svg-container">
  <svg xmlns="https://www.w3.org/2000/svg" xmlns:xlink="https://www.w3.org/1999/xlink"
    xmlns:xml="https://www.w3.org/XML/1998/namespace" xml:space="preserve"
    x="0" y="0" width="400px" height="440px" viewBox="0 0 500 550" >
    <defs>
       <marker id="marker-circle" markerWidth="10" markerHeight="10" refx="5" refy="5">
        <circle cx="5" cy="5" r="3" class="marker"/>
      </marker>
      <marker id="marker-square" markerWidth="7" markerHeight="7" refx="4" refy="4"orient="auto">
        <rect x="1" y="1" width="5" height="5" class="marker"/>
      </marker>
      <marker id="marker-arrow" markerWidth="12" markerHeight="12" refx="6" refy="4" orient="auto">
       <path d="M 1 1 7 4 1 7 Z" class="marker"/>
      </marker>
      <linearGradient id="btn-light" x1="0%" y1="0%" x2="0%" y2="100%" spreadMethod="pad">
        <stop stop-color="hsl(0, 0%, 90%)" offset="0"></stop>
        <stop stop-color="hsl(0, 0%, 92%)" offset="0.05"></stop>
        <stop stop-color="hsl(0, 0%, 97%)" offset="0.33"></stop>
        <stop stop-color="hsl(0, 0%, 87%)" offset="0.67"></stop>
        <stop stop-color="hsl(0, 0%, 84%)" offset="1"></stop>
      </linearGradient>
    </defs>
    <g class="viz">
      <path id="start-path" class="layout-path" d="M210,250 a40,40 0 1,0 80,0 a40,40 0 1,0 -80,0"></path>
      <path id="quad-path" class="layout-path" d="M165,250 a85,85 0 1,0 170,0 a85,85 0 1,0 -170,0"></path>
      <path id="mid-path" class="layout-path" d="M110,250 a140,140 0 1,0 280,0 a140,140 0 1,0 -280,0"></path>
      <path id="end-path" class="layout-path" d="M10,250 a240,240 0 1,0 480,0 a240,240 0 1,0 -480,0"></path>
    </g>
    <g id="cycle-btn" transform="translate(186,518)">
      <rect class="btn-light" x="0" y="0" rx="4" ry="4" width="128" height="32"></rect>
      <text class="btn-light-txt" x="64" y="22">Cycle Colors</text>
    </g>
  </svg>
</div>
<div class="splainin">
    <h2>Styling SVG Markers</h2>
    <p>Using an array of color keys, this demo:</p>
    <ul>
      <li>appends CSS for each color to the stylesheet</li>
      <li>clones svg markers for each color into the defs</li>
      <li>creates a path for each color, with markers</li>
      <li>cycles the CSS color class to the next path</li>
      <li></li>
      <li></li>
    </ul>
    <p><strong><em>Thanks to:</em></strong></p>
    <p>O'Reilly <a href="https://shop.oreilly.com/product/9780596002237.do" target="_blank">SVG essentials</a> for the quadratic beziér curve.</p>
    <p>Jacob Jenkov for <a href="https://tutorials.jenkov.com/svg/marker-element.html" target="_blank">SVG markers</a>.</p>
    <p>David Walsh for <a href="https://davidwalsh.name/add-rules-stylesheets" target="_blank">adding styles</a>.</p>
    <p>complexdan for <a href="https://complexdan.com/svg-circleellipse-to-path-converter/" target="_blank">SVG circles to paths</a>.</p>
    <p><a href="https://plus.google.com/+PaulIrish/posts" target="_blank"><span class="pi">Paul Irish</span></a> for <a href="https://mothereffinghsl.com/" target="_blank"><span class="mef">m</span><span class="mef">o</span><span class="mef">t</span><span class="mef">h</span><span class="mef">e</span><span class="mef">r</span><span class="mef">e</span><span class="mef">f</span><span class="mef">f</span><span class="mef">i</span><span class="mef">n</span><span class="mef">'</span> <span class="mef">h</span><span class="mef">s</span><span class="mef">l</span></a>.</p>
</div>
</div>
<script>
  window.addEventListener('DOMContentLoaded', function () {

"use strict";
      // rainbow starting with blue
    var colors = ['hsl-242', 'hsl-259', 'hsl-273', 'hsl-296', 'hsl-341',
                  'hsl-359', 'hsl-18',  'hsl-35',  'hsl-52',  'hsl-83',
                  'hsl-127', 'hsl-160', 'hsl-190', 'hsl-212', 'hsl-227'];

// add styles to the page for colors and SVG paths
    var addStyles = function () {

// select the <style> tag
      var styles = document.querySelector('#styles');

// select the <style> tag's CSSStyleSheet
      var styleSheet = styles.sheet;

// create styles for the colors, the paths, and the markers
      colors.forEach(function (color) {

var hslColor = color.replace( '-', '(' ) + ', 100%, 50%)';

var colorStyle = '.' + color + ' { stroke: ' + hslColor + '; fill: ' + hslColor + '; color: ' + hslColor+ '; }';

var pathStyle = '.color-path.' + color + ' { ' +
                        'marker-start: url(#marker-circle-' + color + '); ' +
                          'marker-mid: url(#marker-square-' + color + '); ' +
                          'marker-end: url(#marker-arrow-'  + color + '); ' +
                        '; }';

// index 0 to add to the front of the CSSRuleList,
          // to avoid adding !important to the styles already present
        styleSheet.insertRule(pathStyle, 0);
        styleSheet.insertRule(colorStyle, 0);
      });
     };

// create def elements for each color and marker type; append to defs
    var addDefs = function () {

var defs = document.querySelector('defs');

// add the appropriate id to the defs element, add the appropriate class to its marker
      var colorDef = function (def, color) {

// add a color class to the def element's marker child
        var marker = def.querySelector('.marker');
        marker.classList.add(color);

// set the appropriate id on the def element
        def.id = def.id + '-' + color;
      };
      colors.forEach(function (color) {
          // for each color, select and clone the def element for each marker
        var defArray = [];
        defArray.push(defs.querySelector('#marker-circle').cloneNode(true));
        defArray.push(defs.querySelector('#marker-square').cloneNode(true));
        defArray.push(defs.querySelector('#marker-arrow').cloneNode(true));
        defArray.forEach(function (def) {
          colorDef(def, color);
          defs.appendChild(def);
        });
      });
    };
         // create def elements for each color and marker type; append to defs
    var addMefs = function () {
      var forEach = Array.prototype.forEach;
      var mefs = document.querySelectorAll('span.mef');

colors.forEach(function ( color, cx ) {
        if ( mefs[cx] ) {
          mefs[cx].classList.add(color);
        }
      });
    };

// create arrays of x,y objects for the start, middle and end of paths
    var crtCtrlPts = function (markerPos) {
      var ctrlArr = [];
      var ctrlPath = document.querySelector('#' + markerPos + '-path')
      var getPts = function (path) {
        var pathLen = path.getTotalLength();
        var pathPart = 1 / colors.length;
        colors.forEach(function (color, cx) {
          var pathTo = pathLen * ( pathPart * (cx + 1) );
          if ( markerPos === 'quad' ) { pathTo -= 25; }
          var gp = ctrlPath.getPointAtLength( pathTo );
          var pt = { x: Math.round(gp.x), y: Math.round(gp.y) };
          ctrlArr.push(pt);
        });
      };
      getPts(ctrlPath);

return ctrlArr.reverse();
    };

// control points for paths
    var ctrlPts = {
      start : crtCtrlPts('start'),
      quad  : crtCtrlPts('quad'),
      mid   : crtCtrlPts('mid'),
      end   : crtCtrlPts('end')
    };

var crtPaths = function () {
      var viz = document.querySelector('.viz');

var addPath = function(color, cx) {
        var path = document.createElementNS('https://www.w3.org/2000/svg', 'path');
        var pts = {};
        var dString;
        var posArr = Object.keys(ctrlPts);
        posArr.forEach(function (pos) {
          var pt = ctrlPts[pos][cx];
          pts[pos] = pt;
        });
        path.id = 'qp-' + cx;
        dString = 'M ' + pts.start.x + ' ' + pts.start.y +
                 ' Q ' + pts.quad.x + ' ' + pts.quad.y +
                 ', '  + pts.mid.x + ' ' + pts.mid.y +
                 ' T ' + pts.end.x + ' ' + pts.end.y;

path.setAttribute( 'd', dString );
        path.classList.add( 'color-path', color );
        viz.appendChild(path);

};

colors.forEach(function ( color, cx ) { addPath( color, cx ); });
    };

var forEach = Array.prototype.forEach;
    var colorsLength = colors.length;
    var cycleTo;
    var cycleMs = 50;
    var cycleColors = function ( paths, mefs ) {

var nextColor = function(colorClass) {
            var colorX = colors.indexOf(colorClass);
            colorX -= 1;
            if ( colorX < 0 ) { colorX = colors.length -1; }
            return colors[colorX];
          };

forEach.call( paths, function ( path ) {
        var colorClass = path.getAttribute('class')
                             .replace('color-path ', '');
        var nextHsl = nextColor(colorClass);
        path.setAttribute('class', 'color-path ' + nextHsl);
      });
      forEach.call( mefs, function ( mef ) {
        var colorClass = mef.className.replace('mef ', '');
        var nextHsl = nextColor(colorClass);
        mef.className = 'mef ' + nextHsl;
      });
      cycleTo = setTimeout(function () {
        cycleColors( paths, mefs );
      }, cycleMs );
    };

document.querySelector('#cycle-btn').addEventListener('click', function(evt) {
      var cycleTxt = document.querySelector('.btn-light-txt');
      var cycleStr = cycleTxt.innerHTML;
      var paths, mefs;

evt.stopPropagation();
      if ( cycleStr === 'Stop' ) {
        clearTimeout(cycleTo);
        cycleTxt.innerHTML = 'Cycle Colors';
      } else {
        paths = document.querySelectorAll('.viz .color-path');
        mefs = document.querySelectorAll('span.mef');
        cycleTxt.innerHTML = 'Stop';
        cycleTo = setTimeout(function () {
          cycleColors( paths, mefs );
        }, cycleMs );
      }
    });

addStyles();
    addDefs();
    addMefs()
    crtPaths();

});

</script>
</body>
</html>