Get a project point to a closest line in an array of lines

index.js

// http://jsfiddle.net/soulwire/UA6H5/
function projectPointToLine(x, y, x1, y1, x2, y2) {
  const p = {
      x: x,
      y: y
    },
    a = {
      x: x1,
      y: y1
    },
    b = {
      x: x2,
      y: y2
    };
  const atob = {
    x: b.x - a.x,
    y: b.y - a.y
  };
  const atop = {
    x: p.x - a.x,
    y: p.y - a.y
  };
  const len = atob.x * atob.x + atob.y * atob.y;
  let dot = atop.x * atob.x + atop.y * atob.y;
  const t = Math.min(1, Math.max(0, dot / len));

  dot = (b.x - a.x) * (p.y - a.y) - (b.y - a.y) * (p.x - a.x);

  return {
    point: {
      x: a.x + atob.x * t,
      y: a.y + atob.y * t
    },
    left: dot < 1,
    dot: dot,
    t: t
  };
}

// https://stackoverflow.com/a/6853926/3588080
function pointToLineDistance(x, y, x1, y1, x2, y2) {
  const A = x - x1;
  const B = y - y1;
  const C = x2 - x1;
  const D = y2 - y1;

  const dot = A * C + B * D;
  const len_sq = C * C + D * D;
  let param = -1;
  if (len_sq != 0)
    param = dot / len_sq;

  let xx, yy;

  if (param < 0) {
    xx = x1;
    yy = y1;
  } else if (param > 1) {
    xx = x2;
    yy = y2;
  } else {
    xx = x1 + param * C;
    yy = y1 + param * D;
  }

  const dx = x - xx;
  const dy = y - yy;
  return Math.sqrt(dx * dx + dy * dy);
}

function getClosestPointToALine(x, y, fixedLines) {
  const closestLine = getClosestLineToAPoint(x, y, fixedLines);
  return projectPointToLine(x, y, closestLine.x1, closestLine.y1, closestLine.x2, closestLine.y2).point;
}

function getClosestLineToAPoint(x, y, fixedLines) {
  let closestLine, smallestDistance = -999;

  fixedLines.forEach(function(line) {
    if (!closestLine) {
      closestLine = line;
      smallestDistance = pointToLineDistance(x, y, line.x1, line.y1, line.x2, line.y2);
    } else {
      var distance = pointToLineDistance(x, y, line.x1, line.y1, line.x2, line.y2);
      if (distance < smallestDistance) {
        closestLine = line;
        smallestDistance = distance;
      }
    }
  })
  return closestLine;
}

class Line {
  constructor(x1, y1, x2, y2) {
    this.x1 = x1;
    this.y1 = y1;
    this.x2 = x2;
    this.y2 = y2;
  }
}

const fixedLines = [
  new Line(0, 2, 2, 0),
  new Line(0, 0, 0, 2),
  new Line(0, 0, 2, 0)
]

console.log(getClosestPointToALine(0,0,fixedLines)) // {x: 0, y: 0}
console.log(getClosestPointToALine(0,2,fixedLines)) // {x: 0, y: 2}
console.log(getClosestPointToALine(2,0,fixedLines)) // {x: 2, y: 0}