Line, slope intercept form

line-slope-intercept.js

function Line (slope, intercept) {
  this.slope = slope
  this.intercept = intercept
}

function getX (y) {
  y = y || 0
  return (y - this.intercept) / this.slope
}
Line.prototype.getX = getX;

function getY (x) {
  x = x || 0
  return this.slope * x + this.intercept
}
Line.prototype.getY = getY;