Directed Graph Arrowhead

arrowhead.js

// Add svg marker for arrowheads
svg.append('svg:defs').append('svg:marker')
    .attr('id', 'arrowhead')
    .attr('viewBox', '0 0 10 10')
    .attr('refX', 22)
    .attr('refY', 5)
    .attr('markerWidth', 9)
    .attr('markerHeight', 9)
    .attr('orient', 'auto')
  .append('svg:path')
    .attr('d', 'M5 0 L5 10 L10 5 Z')
    .attr('fill', 'rgba(160,160,160,0.9)');

// Add the arrowhead to the link
link = link.enter().append('line')
      .attr('class', 'link')
      .attr('marker-end', 'url(#arrowhead)')