Seamless animated dash

Animating a path's dashed stroke using stroke-dasharray and stroke-dashoffset, similar to this example. This version ensures that there's no little "seam" at the end of a closed path by dynamically setting the dash array and the animation keyframe to a factor of the computed path length.

stroke-dashadjust might make this easier eventually.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8" />
  <style>
    path {
      fill: none;
      stroke: black;
      stroke-width: 2px;
      -webkit-animation: move 0.4s infinite linear;
      -moz-animation: move 0.4s infinite linear;
      animation: move 0.4s infinite linear;
    }

@-webkit-keyframes move {
      0% {
        stroke-dashoffset: 0;
      }
    }

@-moz-keyframes move {
      0% {
        stroke-dashoffset: 0;
      }
    }

@keyframes move {
      0% {
        stroke-dashoffset: 0;
      }
    }

</style>
</head>
<body>
<svg version="1.1" xmlns="https://www.w3.org/2000/svg" width="960" height="500">
  <path d="M636.5,315c-0.4-18.7,1.9-27.9-5.3-35.9
  	c-22.7-25-107.3-2.8-118.3,35.9c-7,24.4,20.6,37.2,16,71c-4,29.6-30.8,60.7-56.5,61.1c-30.8,0.4-32.9-43.8-81.7-70.2
  	c-50.9-27.6-110.1-12.9-125.2-9.2c-66.1,16.4-82.2,56.9-109.2,47.3c-38-13.6-55.9-112.1-19.8-143.5c39-34,121.2,27.7,148.1-3.8
  	c18-21.1,3.1-74.3-25.2-105.3c-31.1-34.1-70.1-32.4-105.3-76.3c-8.2-10.2-16.9-23.8-15.3-39.7c1.2-11.4,7.5-23.3,15.3-29
  	c33.8-25,101.6,62.6,193.1,59.5c40.1-1.3,38.7-18.5,99.2-38.9c126.2-42.6,242.4-4.9,297.7,13c54.7,17.7,105.4,35,129.8,82.4
  	c13,25.3,22.9,67.7,4.6,87c-11.6,12.3-25.1,5.1-46.6,20.6c-2.8,2-28.9,21.4-32.1,49.6c-3.1,27.4,18.7,35,29,70.2
  	c8.8,30.1,8.5,77.8-18.3,99.2c-32.3,25.8-87,0.6-100-5.3c-69.6-32-67.2-88.4-73.3-109.2z"/>
</svg>
<script>

var path = document.querySelector("path"),
      dash = path.getTotalLength() / 100,
      offset = -dash * 2;

// Set the dasharray to something that divides evenly into the total length
  path.style.strokeDasharray = dash + "," + dash;

// Add a 100% keyframe that offsets by one full dash group
  [].slice.call(document.styleSheets).forEach(function(stylesheet){
    [].slice.call(stylesheet.cssRules).forEach(function(rule){
      if (rule.name === "move") {
        rule.appendRule("100% { stroke-dashoffset: " + offset + "; }");
      }
    });
  });

</script>