Determine the aspect ratio of something

aspect-ratio.js

/**
 * Finds the greatest common divisor (GCD) by determining the highest
 * number that evenly divides both numbers
 * @param  {Number} width  Width of the object
 * @param  {Number} height Height of the object
 * @return {Number}        GCD number
 */
const gcd = (width, height) => height === 0 ? width : gcd(height, width % height);

/**
 * Returns the closest aspect ratio from the passed width and height.
 * Takes the GCD and divides both values by that.
 * @param  {Number} width  Width of the object
 * @param  {Number} height Height of the object
 * @return {String}        The closest matching aspect ratio
 *
 * For example:
 * 1024x768 monitor has a GCD of 256.
 * When you divide both values by 256 you get 4x3 or 4:3.
 */
const getAspectRatio = (width, height) => {
  const ratio = gcd(width, height);

  return `${width/ratio}:${height/ratio}`;
};