index.js

/*!
 *
 * arrows
 *
 * MIT
 *
 */

/**
 * Module dependencies.
 */

var Keys = require('keys');
var merge = require('merge');

/**
 * Control flags.
 */

var ctrl = {
  left:  1,
  up:    2,
  right: 4,
  down:  8,
  shoot: 16
};

/**
 * Opposite directions flags.
 */

var opp = {
  1: 4,
  2: 8,
  4: 1,
  8: 2
};

/**
 * Keymap.
 */

var map = {
  37: ctrl.left,
  38: ctrl.up,
  39: ctrl.right,
  40: ctrl.down,
  16: ctrl.shoot, // shift
  17: ctrl.shoot, // ctrl
  88: ctrl.shoot, // x
  90: ctrl.shoot  // z
};

/**
 * Arrows.
 *
 * @return {Object}
 * @api public
 */

module.exports = function(){
  // bitmasks
  var down = 0;
  var keys = 0;

  // construct keys handler using `map`
  var arrows = Keys(map);

  // listen on keystrokes
  arrows.on('keydown', onkeydown);
  arrows.on('keyup', onkeyup);

  /**
   * Returns the `keys` bitmask when evaluated,
   * to use with logical operations.
   *
   * @return {Number} keys
   * @api public
   */

  arrows.valueOf = function(){
    return keys;
  };

  // merge control flags to
  // use with logical operations
  // i.e: arrows & arrows.left && left()
  merge(arrows, ctrl);

  return arrows;

  /**
   * Keydown handler.
   *
   * @param {Event} event
   * @param {Number} key
   * @api private
   */

  function onkeydown(event, key){
    // OR `key`
    keys = down |= key;

    // recent opposite `key` takes precedence
    // so XOR old from the `keys` bitmask
    if (keys & opp[key]) {
      keys ^= opp[key];
    }
  }

  /**
   * Keyup handler.
   *
   * @param {Event} event
   * @param {Number} key
   * @api private
   */

  function onkeyup(event, key){
    // XOR `key`
    keys = down ^= key;
  }
};