You can define the KeyEvent object if it doesn’t exist:
if (typeof KeyEvent == "undefined") {
var KeyEvent = {
DOM_VK_CANCEL: 3,
DOM_VK_HELP: 6,
DOM_VK_BACK_SPACE: 8,
DOM_VK_TAB: 9,
DOM_VK_CLEAR: 12,
DOM_VK_RETURN: 13,
DOM_VK_ENTER: 14,
DOM_VK_SHIFT: 16,
DOM_VK_CONTROL: 17,
DOM_VK_ALT: 18,
DOM_VK_PAUSE: 19,
DOM_VK_CAPS_LOCK: 20,
DOM_VK_ESCAPE: 27,
DOM_VK_SPACE: 32,
DOM_VK_PAGE_UP: 33,
DOM_VK_PAGE_DOWN: 34,
DOM_VK_END: 35,
DOM_VK_HOME: 36,
DOM_VK_LEFT: 37,
DOM_VK_UP: 38,
DOM_VK_RIGHT: 39,
DOM_VK_DOWN: 40,
DOM_VK_PRINTSCREEN: 44,
DOM_VK_INSERT: 45,
DOM_VK_DELETE: 46,
DOM_VK_0: 48,
DOM_VK_1: 49,
DOM_VK_2: 50,
DOM_VK_3: 51,
DOM_VK_4: 52,
DOM_VK_5: 53,
DOM_VK_6: 54,
DOM_VK_7: 55,
DOM_VK_8: 56,
DOM_VK_9: 57,
DOM_VK_SEMICOLON: 59,
DOM_VK_EQUALS: 61,
DOM_VK_A: 65,
DOM_VK_B: 66,
DOM_VK_C: 67,
DOM_VK_D: 68,
DOM_VK_E: 69,
DOM_VK_F: 70,
DOM_VK_G: 71,
DOM_VK_H: 72,
DOM_VK_I: 73,
DOM_VK_J: 74,
DOM_VK_K: 75,
DOM_VK_L: 76,
DOM_VK_M: 77,
DOM_VK_N: 78,
DOM_VK_O: 79,
DOM_VK_P: 80,
DOM_VK_Q: 81,
DOM_VK_R: 82,
DOM_VK_S: 83,
DOM_VK_T: 84,
DOM_VK_U: 85,
DOM_VK_V: 86,
DOM_VK_W: 87,
DOM_VK_X: 88,
DOM_VK_Y: 89,
DOM_VK_Z: 90,
DOM_VK_CONTEXT_MENU: 93,
DOM_VK_NUMPAD0: 96,
DOM_VK_NUMPAD1: 97,
DOM_VK_NUMPAD2: 98,
DOM_VK_NUMPAD3: 99,
DOM_VK_NUMPAD4: 100,
DOM_VK_NUMPAD5: 101,
DOM_VK_NUMPAD6: 102,
DOM_VK_NUMPAD7: 103,
DOM_VK_NUMPAD8: 104,
DOM_VK_NUMPAD9: 105,
DOM_VK_MULTIPLY: 106,
DOM_VK_ADD: 107,
DOM_VK_SEPARATOR: 108,
DOM_VK_SUBTRACT: 109,
DOM_VK_DECIMAL: 110,
DOM_VK_DIVIDE: 111,
DOM_VK_F1: 112,
DOM_VK_F2: 113,
DOM_VK_F3: 114,
DOM_VK_F4: 115,
DOM_VK_F5: 116,
DOM_VK_F6: 117,
DOM_VK_F7: 118,
DOM_VK_F8: 119,
DOM_VK_F9: 120,
DOM_VK_F10: 121,
DOM_VK_F11: 122,
DOM_VK_F12: 123,
DOM_VK_F13: 124,
DOM_VK_F14: 125,
DOM_VK_F15: 126,
DOM_VK_F16: 127,
DOM_VK_F17: 128,
DOM_VK_F18: 129,
DOM_VK_F19: 130,
DOM_VK_F20: 131,
DOM_VK_F21: 132,
DOM_VK_F22: 133,
DOM_VK_F23: 134,
DOM_VK_F24: 135,
DOM_VK_NUM_LOCK: 144,
DOM_VK_SCROLL_LOCK: 145,
DOM_VK_COMMA: 188,
DOM_VK_PERIOD: 190,
DOM_VK_SLASH: 191,
DOM_VK_BACK_QUOTE: 192,
DOM_VK_OPEN_BRACKET: 219,
DOM_VK_BACK_SLASH: 220,
DOM_VK_CLOSE_BRACKET: 221,
DOM_VK_QUOTE: 222,
DOM_VK_META: 224
};
}
See also KeyEvent in DOM Level 3.