iron-a11y-keys-behavior.html

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<link rel="import" href="../polymer/polymer.html">

<script>
  (function() {
    'use strict';

    /**
     * Chrome uses an older version of DOM Level 3 Keyboard Events
     *
     * Most keys are labeled as text, but some are Unicode codepoints.
     * Values taken from: http://www.w3.org/TR/2007/WD-DOM-Level-3-Events-20071221/keyset.html#KeySet-Set
     */
    var KEY_IDENTIFIER = {
      'U+0008': 'backspace',
      'U+0009': 'tab',
      'U+001B': 'esc',
      'U+0020': 'space',
      'U+007F': 'del'
    };

    /**
     * Special table for KeyboardEvent.keyCode.
     * KeyboardEvent.keyIdentifier is better, and KeyBoardEvent.key is even better
     * than that.
     *
     * Values from: https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent.keyCode#Value_of_keyCode
     */
    var KEY_CODE = {
      8: 'backspace',
      9: 'tab',
      13: 'enter',
      27: 'esc',
      33: 'pageup',
      34: 'pagedown',
      35: 'end',
      36: 'home',
      32: 'space',
      37: 'left',
      38: 'up',
      39: 'right',
      40: 'down',
      46: 'del',
      106: '*'
    };

    /**
     * MODIFIER_KEYS maps the short name for modifier keys used in a key
     * combo string to the property name that references those same keys
     * in a KeyboardEvent instance.
     */
    var MODIFIER_KEYS = {
      'shift': 'shiftKey',
      'ctrl': 'ctrlKey',
      'alt': 'altKey',
      'meta': 'metaKey'
    };

    /**
     * KeyboardEvent.key is mostly represented by printable character made by
     * the keyboard, with unprintable keys labeled nicely.
     *
     * However, on OS X, Alt+char can make a Unicode character that follows an
     * Apple-specific mapping. In this case, we fall back to .keyCode.
     */
    var KEY_CHAR = /[a-z0-9*]/;

    /**
     * Matches a keyIdentifier string.
     */
    var IDENT_CHAR = /U\+/;

    /**
     * Matches arrow keys in Gecko 27.0+
     */
    var ARROW_KEY = /^arrow/;

    /**
     * Matches space keys everywhere (notably including IE10's exceptional name
     * `spacebar`).
     */
    var SPACE_KEY = /^space(bar)?/;

    /**
     * Matches ESC key.
     *
     * Value from: http://w3c.github.io/uievents-key/#key-Escape
     */
    var ESC_KEY = /^escape$/;

    /**
     * Transforms the key.
     * @param {string} key The KeyBoardEvent.key
     * @param {Boolean} [noSpecialChars] Limits the transformation to
     * alpha-numeric characters.
     */
    function transformKey(key, noSpecialChars) {
      var validKey = '';
      if (key) {
        var lKey = key.toLowerCase();
        if (lKey === ' ' || SPACE_KEY.test(lKey)) {
          validKey = 'space';
        } else if (ESC_KEY.test(lKey)) {
          validKey = 'esc';
        } else if (lKey.length == 1) {
          if (!noSpecialChars || KEY_CHAR.test(lKey)) {
            validKey = lKey;
          }
        } else if (ARROW_KEY.test(lKey)) {
          validKey = lKey.replace('arrow', '');
        } else if (lKey == 'multiply') {
          // numpad '*' can map to Multiply on IE/Windows
          validKey = '*';
        } else {
          validKey = lKey;
        }
      }
      return validKey;
    }

    function transformKeyIdentifier(keyIdent) {
      var validKey = '';
      if (keyIdent) {
        if (keyIdent in KEY_IDENTIFIER) {
          validKey = KEY_IDENTIFIER[keyIdent];
        } else if (IDENT_CHAR.test(keyIdent)) {
          keyIdent = parseInt(keyIdent.replace('U+', '0x'), 16);
          validKey = String.fromCharCode(keyIdent).toLowerCase();
        } else {
          validKey = keyIdent.toLowerCase();
        }
      }
      return validKey;
    }

    function transformKeyCode(keyCode) {
      var validKey = '';
      if (Number(keyCode)) {
        if (keyCode >= 65 && keyCode <= 90) {
          // ascii a-z
          // lowercase is 32 offset from uppercase
          validKey = String.fromCharCode(32 + keyCode);
        } else if (keyCode >= 112 && keyCode <= 123) {
          // function keys f1-f12
          validKey = 'f' + (keyCode - 112);
        } else if (keyCode >= 48 && keyCode <= 57) {
          // top 0-9 keys
          validKey = String(keyCode - 48);
        } else if (keyCode >= 96 && keyCode <= 105) {
          // num pad 0-9
          validKey = String(keyCode - 96);
        } else {
          validKey = KEY_CODE[keyCode];
        }
      }
      return validKey;
    }

    /**
      * Calculates the normalized key for a KeyboardEvent.
      * @param {KeyboardEvent} keyEvent
      * @param {Boolean} [noSpecialChars] Set to true to limit keyEvent.key
      * transformation to alpha-numeric chars. This is useful with key
      * combinations like shift + 2, which on FF for MacOS produces
      * keyEvent.key = @
      * To get 2 returned, set noSpecialChars = true
      * To get @ returned, set noSpecialChars = false
     */
    function normalizedKeyForEvent(keyEvent, noSpecialChars) {
      // Fall back from .key, to .keyIdentifier, to .keyCode, and then to
      // .detail.key to support artificial keyboard events.
      return transformKey(keyEvent.key, noSpecialChars) ||
        transformKeyIdentifier(keyEvent.keyIdentifier) ||
        transformKeyCode(keyEvent.keyCode) ||
        transformKey(keyEvent.detail ? keyEvent.detail.key : keyEvent.detail, noSpecialChars) || '';
    }

    function keyComboMatchesEvent(keyCombo, event) {
      // For combos with modifiers we support only alpha-numeric keys
      var keyEvent = normalizedKeyForEvent(event, keyCombo.hasModifiers);
      return keyEvent === keyCombo.key &&
        (!keyCombo.hasModifiers || (
          !!event.shiftKey === !!keyCombo.shiftKey &&
          !!event.ctrlKey === !!keyCombo.ctrlKey &&
          !!event.altKey === !!keyCombo.altKey &&
          !!event.metaKey === !!keyCombo.metaKey)
        );
    }

    function parseKeyComboString(keyComboString) {
      if (keyComboString.length === 1) {
        return {
          combo: keyComboString,
          key: keyComboString,
          event: 'keydown'
        };
      }
      return keyComboString.split('+').reduce(function(parsedKeyCombo, keyComboPart) {
        var eventParts = keyComboPart.split(':');
        var keyName = eventParts[0];
        var event = eventParts[1];

        if (keyName in MODIFIER_KEYS) {
          parsedKeyCombo[MODIFIER_KEYS[keyName]] = true;
          parsedKeyCombo.hasModifiers = true;
        } else {
          parsedKeyCombo.key = keyName;
          parsedKeyCombo.event = event || 'keydown';
        }

        return parsedKeyCombo;
      }, {
        combo: keyComboString.split(':').shift()
      });
    }

    function parseEventString(eventString) {
      return eventString.trim().split(' ').map(function(keyComboString) {
        return parseKeyComboString(keyComboString);
      });
    }

    /**
     * `Polymer.IronA11yKeysBehavior` provides a normalized interface for processing
     * keyboard commands that pertain to [WAI-ARIA best practices](http://www.w3.org/TR/wai-aria-practices/#kbd_general_binding).
     * The element takes care of browser differences with respect to Keyboard events
     * and uses an expressive syntax to filter key presses.
     *
     * Use the `keyBindings` prototype property to express what combination of keys
     * will trigger the event to fire.
     *
     * Use the `key-event-target` attribute to set up event handlers on a specific
     * node.
     * The `keys-pressed` event will fire when one of the key combinations set with the
     * `keys` property is pressed.
     *
     * @demo demo/index.html
     * @polymerBehavior
     */
    Polymer.IronA11yKeysBehavior = {
      properties: {
        /**
         * The HTMLElement that will be firing relevant KeyboardEvents.
         * @type {!EventTarget}
         */
        keyEventTarget: {
          type: Object,
          value: function() {
            return this;
          }
        },

        /**
         * If true, this property will cause the implementing element to
         * automatically stop propagation on any handled KeyboardEvents.
         */
        stopKeyboardEventPropagation: {
          type: Boolean,
          value: false
        },

        _boundKeyHandlers: {
          type: Array,
          value: function() {
            return [];
          }
        },

        // We use this due to a limitation in IE10 where instances will have
        // own properties of everything on the "prototype".
        _imperativeKeyBindings: {
          type: Object,
          value: function() {
            return {};
          }
        }
      },

      observers: [
        '_resetKeyEventListeners(keyEventTarget, _boundKeyHandlers)'
      ],

      keyBindings: {},

      registered: function() {
        this._prepKeyBindings();
      },

      attached: function() {
        this._listenKeyEventListeners();
      },

      detached: function() {
        this._unlistenKeyEventListeners();
      },

      /**
       * Can be used to imperatively add a key binding to the implementing
       * element. This is the imperative equivalent of declaring a keybinding
       * in the `keyBindings` prototype property.
       */
      addOwnKeyBinding: function(eventString, handlerName) {
        this._imperativeKeyBindings[eventString] = handlerName;
        this._prepKeyBindings();
        this._resetKeyEventListeners();
      },

      /**
       * When called, will remove all imperatively-added key bindings.
       */
      removeOwnKeyBindings: function() {
        this._imperativeKeyBindings = {};
        this._prepKeyBindings();
        this._resetKeyEventListeners();
      },

      /**
       * Returns true if a keyboard event matches `eventString`.
       *
       * @param {KeyboardEvent} event
       * @param {string} eventString
       * @return {boolean}
       */
      keyboardEventMatchesKeys: function(event, eventString) {
        var keyCombos = parseEventString(eventString);
        for (var i = 0; i < keyCombos.length; ++i) {
          if (keyComboMatchesEvent(keyCombos[i], event)) {
            return true;
          }
        }
        return false;
      },

      _collectKeyBindings: function() {
        var keyBindings = this.behaviors.map(function(behavior) {
          return behavior.keyBindings;
        });

        if (keyBindings.indexOf(this.keyBindings) === -1) {
          keyBindings.push(this.keyBindings);
        }

        return keyBindings;
      },

      _prepKeyBindings: function() {
        this._keyBindings = {};

        this._collectKeyBindings().forEach(function(keyBindings) {
          for (var eventString in keyBindings) {
            this._addKeyBinding(eventString, keyBindings[eventString]);
          }
        }, this);

        for (var eventString in this._imperativeKeyBindings) {
          this._addKeyBinding(eventString, this._imperativeKeyBindings[eventString]);
        }

        // Give precedence to combos with modifiers to be checked first.
        for (var eventName in this._keyBindings) {
          this._keyBindings[eventName].sort(function (kb1, kb2) {
            var b1 = kb1[0].hasModifiers;
            var b2 = kb2[0].hasModifiers;
            return (b1 === b2) ? 0 : b1 ? -1 : 1;
          })
        }
      },

      _addKeyBinding: function(eventString, handlerName) {
        parseEventString(eventString).forEach(function(keyCombo) {
          this._keyBindings[keyCombo.event] =
            this._keyBindings[keyCombo.event] || [];

          this._keyBindings[keyCombo.event].push([
            keyCombo,
            handlerName
          ]);
        }, this);
      },

      _resetKeyEventListeners: function() {
        this._unlistenKeyEventListeners();

        if (this.isAttached) {
          this._listenKeyEventListeners();
        }
      },

      _listenKeyEventListeners: function() {
        Object.keys(this._keyBindings).forEach(function(eventName) {
          var keyBindings = this._keyBindings[eventName];
          var boundKeyHandler = this._onKeyBindingEvent.bind(this, keyBindings);

          this._boundKeyHandlers.push([this.keyEventTarget, eventName, boundKeyHandler]);

          this.keyEventTarget.addEventListener(eventName, boundKeyHandler);
        }, this);
      },

      _unlistenKeyEventListeners: function() {
        var keyHandlerTuple;
        var keyEventTarget;
        var eventName;
        var boundKeyHandler;

        while (this._boundKeyHandlers.length) {
          // My kingdom for block-scope binding and destructuring assignment..
          keyHandlerTuple = this._boundKeyHandlers.pop();
          keyEventTarget = keyHandlerTuple[0];
          eventName = keyHandlerTuple[1];
          boundKeyHandler = keyHandlerTuple[2];

          keyEventTarget.removeEventListener(eventName, boundKeyHandler);
        }
      },

      _onKeyBindingEvent: function(keyBindings, event) {
        if (this.stopKeyboardEventPropagation) {
          event.stopPropagation();
        }

        // if event has been already prevented, don't do anything
        if (event.defaultPrevented) {
          return;
        }

        for (var i = 0; i < keyBindings.length; i++) {
          var keyCombo = keyBindings[i][0];
          var handlerName = keyBindings[i][1];
          if (keyComboMatchesEvent(keyCombo, event)) {
            this._triggerKeyHandler(keyCombo, handlerName, event);
            // exit the loop if eventDefault was prevented
            if (event.defaultPrevented) {
              return;
            }
          }
        }
      },

      _triggerKeyHandler: function(keyCombo, handlerName, keyboardEvent) {
        var detail = Object.create(keyCombo);
        detail.keyboardEvent = keyboardEvent;
        var event = new CustomEvent(keyCombo.event, {
          detail: detail,
          cancelable: true
        });
        this[handlerName].call(this, event);
        if (event.defaultPrevented) {
          keyboardEvent.preventDefault();
        }
      }
    };
  })();
</script>