2D Point to Line Segment distance function

point-to-line-2d.js

// Taken From:
// https://stackoverflow.com/questions/849211/shortest-distance-between-a-point-and-a-line-segment

function sqr (x) {
  return x * x;
}

function dist2 (v, w) {
  return sqr(v[0] - w[0]) + sqr(v[1] - w[1]);
}

// p - point
// v - start point of segment
// w - end point of segment
function distToSegmentSquared (p, v, w) {
  var l2 = dist2(v, w);
  if (l2 === 0) return dist2(p, v);
  var t = ((p[0] - v[0]) * (w[0] - v[0]) + (p[1] - v[1]) * (w[1] - v[1])) / l2;
  t = Math.max(0, Math.min(1, t));
  return dist2(p, [ v[0] + t * (w[0] - v[0]), v[1] + t * (w[1] - v[1]) ]);
}

// p - point
// v - start point of segment
// w - end point of segment
function distToSegment (p, v, w) {
  return Math.sqrt(distToSegmentSquared(p, v, w));
}

module.exports = distToSegment;
module.exports.squared = distToSegmentSquared;

Handy snippet thanks!
Here's the same thing modified to reuse partial results and accept data structures instead of lists:

    function dist(point, x, y)
    {
        var dx = x - point.x;
        var dy = y - point.y;
        return Math.sqrt(dx * dx + dy * dy);
    }

    // point - { x, y }
    // line - { sx, sy, ex, ey }
    function distToSegment(point, line)
    {
        var dx = line.ex - line.sx;
        var dy = line.ey - line.sy;
        var l2 = dx * dx + dy * dy;
        
        if (l2 == 0)
            return this.dist(point, line.sx, line.sy);

        var t = ((point.x - line.sx) * dx + (point.y - line.sy) * dy) / l2;
        t = Math.max(0, Math.min(1, t));

        return this.dist(point, line.sx + t * dx, line.sy + t * dy);
    }