gistfile1.js

/**
 * Handles converting a magnitude from one unit to another.
 * @module convert
 */

const CONVERSION_TABLE = {
  m: { ft: 3.2808 }, // elevation
  km: { mi: .62137 }, // distance
  kcal: { kj: 4.1868 }, // energy
  kph: { mph: .62137 }, // speed
  kg: { lb: 2.2046 }, // weight
  'min/km': { 'min/mi': 1.60934 } // pace
};

/**
 * Creates a new conversion object, but not intened to be used with the `new`
 * keyword. Not intended to be used by itself, but instead to chain additional
 * methods.
 * @param  {number} magnitude - the initial value of the magnitude
 * @return {object} the `convert` instance
 */
function convert (magnitude) {
  this.initialMagnitude = magnitude;
  return this;
};

/**
 * Specify the unit of the magnitude parameter passed to `convert()`. Only
 * intended to be used when chained to `convert()`.
 *   example: convert(1).from('mi')
 * @param  {string} unit - describes the unit, like `mi` or `km`
 * @return {object} - the convert instance
 */
convert.prototype.from = function (unit) {
  this.rawInitialUnit = unit;
  this.initialUnit = this.rawInitialUnit.toLowerCase();
  return this;
};

/**
 * Specify the unit to which to convert the magnitude. Only intended to be used
 * when chained to `from()`.
 *   example: convert(1).from('mi').to('km')
 * @param  {string} unit - describes the ouput unit after conversion
 * @return {number} - the resulting magnitude from the conversion
 */
convert.prototype.to = function (unit) {
  let multiplier;
  this.rawResultUnit = unit;
  this.resultUnit = this.rawResultUnit.toLowerCase();
  if (this.initialUnit === this.resultUnit) {
    multiplier = 1;
  } else if (this.initialUnit in CONVERSION_TABLE) {
    multiplier = CONVERSION_TABLE[this.initialUnit][this.resultUnit];
  } else if (this.resultUnit in CONVERSION_TABLE) {
    multiplier = 1 / CONVERSION_TABLE[this.resultUnit.][this.initialUnit];
  }
  return this.initialMagnitude * multiplier;
};

export default new convert();