经常我们需要捕捉键盘的动作，比如按了什么键。
好处，你懂得的。
兼容IE和firefox的js。
document.onkeydown=function(evt)
{
var evt=window.event?window.event:evt;
if(evt.keyCode==13)
{
alert("你按了回车键！");
}
};
下面是keycode的对应：
event.keycode值大全
1 keycode 8 = BackSpace BackSpace
2 keycode 9 = Tab Tab
3 keycode 12 = Clear
4 keycode 13 = Enter
5 keycode 16 = Shift_L
6 keycode 17 = Control_L
7 keycode 18 = Alt_L
8 keycode 19 = Pause
9 keycode 20 = Caps_Lock
10 keycode 27 = Escape Escape
11 keycode 32 = space space
12 keycode 33 = Prior
13 keycode 34 = Next
14 keycode 35 = End
15 keycode 36 = Home
16 keycode 37 = Left
17 keycode 38 = Up
18 keycode 39 = Right
19 keycode 40 = Down
20 keycode 41 = Select
21 keycode 42 = Print
22 keycode 43 = Execute
23 keycode 45 = Insert
24 keycode 46 = Delete
25 keycode 47 = Help
26 keycode 48 = 0 equal braceright
27 keycode 49 = 1 exclam onesuperior
28 keycode 50 = 2 quotedbl twosuperior
29 keycode 51 = 3 section threesuperior
30 keycode 52 = 4 dollar
31 keycode 53 = 5 percent
32 keycode 54 = 6 ampersand
33 keycode 55 = 7 slash braceleft
34 keycode 56 = 8 parenleft bracketleft
35 keycode 57 = 9 parenright bracketright
36 keycode 65 = a A
37 keycode 66 = b B
38 keycode 67 = c C
39 keycode 68 = d D
40 keycode 69 = e E EuroSign
41 keycode 70 = f F
42
43 keycode 71 = g G
44 keycode 72 = h H
45 keycode 73 = i I
46 keycode 74 = j J
47 keycode 75 = k K
48 keycode 76 = l L
49 keycode 77 = m M mu
50 keycode 78 = n N
51 keycode 79 = o O
52 keycode 80 = p P
53 keycode 81 = q Q at
54 keycode 82 = r R
55 keycode 83 = s S
56 keycode 84 = t T
57 keycode 85 = u U
58 keycode 86 = v V
59 keycode 87 = w W
60 keycode 88 = x X
61 keycode 89 = y Y
62 keycode 90 = z Z
63 keycode 96 = KP_0 KP_0
64 keycode 97 = KP_1 KP_1
65 keycode 98 = KP_2 KP_2
66 keycode 99 = KP_3 KP_3
67 keycode 100 = KP_4 KP_4
68 keycode 101 = KP_5 KP_5
69 keycode 102 = KP_6 KP_6
70 keycode 103 = KP_7 KP_7
71 keycode 104 = KP_8 KP_8
72 keycode 105 = KP_9 KP_9
73 keycode 106 = KP_Multiply KP_Multiply
74 keycode 107 = KP_Add KP_Add
75
76 keycode 108 = KP_Separator KP_Separator
77 keycode 109 = KP_Subtract KP_Subtract
78 keycode 110 = KP_Decimal KP_Decimal
79 keycode 111 = KP_Divide KP_Divide
80 keycode 112 = F1
81 keycode 113 = F2
82 keycode 114 = F3
83 keycode 115 = F4
84
85
86 keycode 116 = F5
87 keycode 117 = F6
88 keycode 118 = F7
89 keycode 119 = F8
90 keycode 120 = F9
91 keycode 121 = F10
92 keycode 122 = F11
93 keycode 123 = F12
94 keycode 124 = F13
95 keycode 125 = F14
96 keycode 126 = F15
97 keycode 127 = F16
98 keycode 128 = F17
99 keycode 129 = F18
100 keycode 130 = F19
101 keycode 131 = F20
102 keycode 132 = F21
103 keycode 133 = F22
104 keycode 134 = F23
105 keycode 135 = F24
106 keycode 136 = Num_Lock
107 keycode 137 = Scroll_Lock
108 keycode 187 = acute grave
109 keycode 188 = comma semicolon
110 keycode 189 = minus underscore
111 keycode 190 = period colon
112 keycode 192 = numbersign apostrophe
113 keycode 210 = plusminus hyphen macron
114 keycode 211 =
115 keycode 212 = copyright registered
116 keycode 213 = guillemotleft guillemotright
117 keycode 214 = masculine ordfeminine
118 keycode 215 = ae AE
119 keycode 216 = cent yen
120 keycode 217 = questiondown exclamdown
121 keycode 218 = onequarter onehalf threequarters
122 keycode 220 = less greater bar
123 keycode 221 = plus asterisk asciitilde
124 keycode 227 = multiply division
125
126 keycode 228 = acircumflex Acircumflex
127 keycode 229 = ecircumflex Ecircumflex
128 keycode 230 = icircumflex Icircumflex
129 keycode 231 = ocircumflex Ocircumflex
130 keycode 232 = ucircumflex Ucircumflex
131 keycode 233 = ntilde Ntilde
132 keycode 234 = yacute Yacute
133 keycode 235 = oslash Ooblique
134 keycode 236 = aring Aring
135 keycode 237 = ccedilla Ccedilla
136 keycode 238 = thorn THORN
137 keycode 239 = eth ETH
138 keycode 240 = diaeresis cedilla currency
139 keycode 241 = agrave Agrave atilde Atilde
140 keycode 242 = egrave Egrave
141 keycode 243 = igrave Igrave
142 keycode 244 = ograve Ograve otilde Otilde
143 keycode 245 = ugrave Ugrave
144 keycode 246 = adiaeresis Adiaeresis
145 keycode 247 = ediaeresis Ediaeresis
146 keycode 248 = idiaeresis Idiaeresis
147 keycode 249 = odiaeresis Odiaeresis
148 keycode 250 = udiaeresis Udiaeresis
149 keycode 251 = ssharp question backslash
150 keycode 252 = asciicircum degree
151 keycode 253 = 3 sterling
152 keycode 254 = Mode_switch
153
154 使用event对象的keyCode属性判断输入的键值
155 eg：if(event.keyCode==13)alert(“enter!”);
156 键值对应表
157 A 0X65 U 0X85
158 B 0X66 V 0X86
159 C 0X67 W 0X87
160 D 0X68 X 0X88
161 E 0X69 Y 0X89
162 F 0X70 Z 0X90
163 G 0X71 0 0X48
164 H 0X72 1 0X49
165 I 0X73 2 0X50
166 J 0X74 3 0X51
167 K 0X75 4 0X52
168 L 0X76 5 0X53
169 M 0X77 6 0X54
170 N 0X78 7 0X55
171 O 0X79 8 0X56
172 P 0X80 9 0X57
173 Q 0X81 ESC 0X1B
174 R 0X82 CTRL 0X11
175 S 0X83 SHIFT 0X10
176 T 0X84 ENTER 0XD
177
178
如果要使用组合键，则可以利用event.ctrlKey，event.shiftKey，event .altKey判断是否按下了ctrl键、shift键以及alt