example.js

var Robot = (function () {
  'use strict';

  var VALID_DIRECTIONS = ['north', 'east', 'south', 'west'];
  var INSTRUCTION_KEYS = {
    A: 'advance',
    L: 'turnLeft',
    R: 'turnRight'
  };

  function Robot() {
    this.coordinates = [0, 0];
    this.bearing = 'north';
  }

  Robot.prototype.at = function (x, y) {
    this.coordinates = [x, y];
  };

  Robot.prototype.orient = function (direction) {
    if (VALID_DIRECTIONS.indexOf(direction) === -1) {
      throw new Error('Invalid Robot Bearing');
    }

    this.bearing = direction;
  };

  Robot.prototype.advance = function () {
    switch (this.bearing) {
    case 'north':
      this.coordinates[1]++;
      break;
    case 'east':
      this.coordinates[0]++;
      break;
    case 'south':
      this.coordinates[1]--;
      break;
    case 'west':
      this.coordinates[0]--;
      break;
    }
  };

  Robot.prototype.turnLeft = function () {
    var directionPosition = VALID_DIRECTIONS.indexOf(this.bearing);

    if (directionPosition > 0) {
      this.orient(VALID_DIRECTIONS[--directionPosition]);
    } else {
      this.orient(VALID_DIRECTIONS[VALID_DIRECTIONS.length - 1]);
    }
  };

  Robot.prototype.turnRight = function () {
    var directionPosition = VALID_DIRECTIONS.indexOf(this.bearing);

    if (directionPosition < (VALID_DIRECTIONS.length - 1)) {
      this.orient(VALID_DIRECTIONS[++directionPosition]);
    } else {
      this.orient(VALID_DIRECTIONS[0]);
    }
  };

  Robot.prototype.instructions = function (instructionKeys) {
    return instructionKeys.split('')
      .map(function (key) {
        return INSTRUCTION_KEYS[key];
      });
  };

  Robot.prototype.place = function (args) {
    this.coordinates = [args.x, args.y];
    this.bearing = args.direction;
  };

  Robot.prototype.evaluate = function (instructionKeys) {
    this.instructions(instructionKeys)
      .forEach(function (instruction) {
        this[instruction]();
      }, this);
  };

  return Robot;
})();

module.exports = Robot;