How can I animate a progressive drawing of svg path?

There are three techniques listed in this answer:

---

There is an all-SVG solution that involves progressively modifying the stroke-dasharray for the shape to draw a longer and longer ‘dash’ followed by an enormous gap.

Demo: http://phrogz.net/svg/progressively-drawing-svg-path-via-dasharray.html

Relevant code:

var distancePerPoint = 1;
var drawFPS          = 60;

var orig = document.querySelector('path'), length, timer;
orig.addEventListener('mouseover',startDrawingPath,false);
orig.addEventListener('mouseout', stopDrawingPath, false);

function startDrawingPath(){
  length = 0;
  orig.style.stroke="#f60";
  timer = setInterval(increaseLength,1000/drawFPS);
}

function increaseLength(){
  var pathLength = orig.getTotalLength();
  length += distancePerPoint;
  orig.style.strokeDasharray = [length,pathLength].join(' ');
  if (length >= pathLength) clearInterval(timer);
}

function stopDrawingPath(){
  clearInterval(timer);
  orig.style.stroke="";
  orig.style.strokeDasharray = '';
}

---

Alternatively, you can still use all SVG and choose to build the SVG path one command at a time:

Demo: http://phrogz.net/svg/progressively-cloning-svg-path.html

Relevant code:

// Assumes 'orig' and dup' are SVG paths
function addNextPathSegment(){
  var nextIndex   = dup.pathSegList.numberOfItems;
  if (nextIndex<orig.pathSegList.numberOfItems){
    var nextSegment = orig.pathSegList.getItem(nextIndex);
    var segmentDup  = cloneSVGPathSeg( dup, nextSegment );
    dup.pathSegList.appendItem( segmentDup );
  }
}

function cloneSVGPathSeg( path, seg ){
  switch(seg.pathSegTypeAsLetter){
    case 'M': return path.createSVGPathSegMovetoAbs(seg.x,seg.y);                                                     break;
    case 'm': return path.createSVGPathSegMovetoRel(seg.x,seg.y);                                                     break;
    case 'L': return path.createSVGPathSegLinetoAbs(seg.x,seg.y);                                                     break;
    case 'l': return path.createSVGPathSegLinetoRel(seg.x,seg.y);                                                     break;
    case 'H': return path.createSVGPathSegLinetoHorizontalAbs(seg.x);                                                 break;
    case 'h': return path.createSVGPathSegLinetoHorizontalRel(seg.x);                                                 break;
    case 'V': return path.createSVGPathSegLinetoVerticalAbs(seg.y);                                                   break;
    case 'v': return path.createSVGPathSegLinetoVerticalRel(seg.y);                                                   break;
    case 'C': return path.createSVGPathSegCurvetoCubicAbs(seg.x,seg.y,seg.x1,seg.y1,seg.x2,seg.y2);                   break;
    case 'c': return path.createSVGPathSegCurvetoCubicRel(seg.x,seg.y,seg.x1,seg.y1,seg.x2,seg.y2);                   break;
    case 'S': return path.createSVGPathSegCurvetoCubicSmoothAbs(seg.x,seg.y,seg.x2,seg.y2);                           break;
    case 's': return path.createSVGPathSegCurvetoCubicSmoothRel(seg.x,seg.y,seg.x2,seg.y2);                           break;
    case 'Q': return path.createSVGPathSegCurvetoQuadraticAbs(seg.x,seg.y,seg.x1,seg.y1);                             break;
    case 'q': return path.createSVGPathSegCurvetoQuadraticRel(seg.x,seg.y,seg.x1,seg.y1);                             break;
    case 'T': return path.createSVGPathSegCurvetoQuadraticSmoothAbs(seg.x,seg.y);                                     break;
    case 't': return path.createSVGPathSegCurvetoQuadraticSmoothRel(seg.x,seg.y);                                     break;
    case 'A': return path.createSVGPathSegArcAbs(seg.x,seg.y,seg.r1,seg.r2,seg.angle,seg.largeArcFlag,seg.sweepFlag); break;
    case 'a': return path.createSVGPathSegArcRel(seg.x,seg.y,seg.r1,seg.r2,seg.angle,seg.largeArcFlag,seg.sweepFlag); break;
    case 'z':
    case 'Z': return path.createSVGPathSegClosePath();                                                                break;
  }
}

---

Finally, you may choose to draw your path to an HTML5 canvas by sampling the SVG path periodically and drawing to the canvas. (Note that the SVG path does not need to be displayed for this to happen; you can build an SVG path element entirely in JavaScript and sample it):

Demo: http://phrogz.net/svg/progressively-drawing-svg-path.html

Relevant code:

function startDrawingPath(){
  points = [];
  timer = setInterval(buildPath,1000/drawFPS);
}

// Assumes that 'orig' is an SVG path
function buildPath(){
  var nextPoint = points.length * distancePerPoint;
  var pathLength = orig.getTotalLength();
  if (nextPoint <= pathLength){
    points.push(orig.getPointAtLength(nextPoint));
    redrawCanvas();
  } else stopDrawingPath();
}

function redrawCanvas(){
  clearCanvas();
  ctx.beginPath();
  ctx.moveTo(points[0].x,points[0].y);
  for (var i=1;i<points.length;i++) ctx.lineTo(points[i].x,points[i].y);
  ctx.stroke();
}