js位运行符的运用。
js运算符的使用技巧。
是否包含指定字符：
~
~"str1".indexOf("str2")
str1
被查找的字符串
str2
查找的字符串
如果
str1
不含有
str2
，则返回数字
0
。
例：
var
str1='abc'
var
str2='a'
if(~str1.indexOf(str2)){
console.log('有'+str2)
//有a
}else{
console.log('无'+str2)
}
取整：
|
num
|
0
num
整数
例：
1.3
|
0
//1
取半：
>>
num
>>
1
num
整数
例：求
50
的
1/2
50
>>
1
//25
有除号
/
干嘛不用呢？多好呀：
50/2
//25
成长值评级：
||
需求1：
成长值为5是1星；
成长值为10是2星；
成长值为12是3星；
成长值为15是4星；
其他都是0星。
({'5':1,'10':2,'12':3,'15':4}[val]
||
0)
val
成长值。
判断奇偶：
&
num
&
1
num
整数
例：
var
num=3
if
(num
&
1)
{
console.log("num是奇数")
//num是奇数
}
else
{
console.log("num是偶数")
}
交换两个数字的值：
^=
使用位运行符：
var
num1
=
1,
num2
=
2
num1
^=
num2
num2
^=
num1
num1
^=
num2
console.log(num1,num2)
//2
1
使用数组：
var
num1
=
1,
num2
=
2
num1
=
[num2,
num2
=
num1][0]
console.log(num1,num2)
//2
1
2的n次方：
<<
和
**
1
<<
n-1
使用位运行符：
2的n次方
例：2的3次方：1<<3
//8
使用幂运行符：
个人觉得这个不如直接使用
幂
的方式好。
x的y次方：
x**y
例：2的3次方：2**3
//8
方法比较：
使用
<<
的方式可以支持负数，**
需要用括号否则出错。
使用
**
比较直观，没研究过
<<
方法的任意数的任意次方的规律。
1<<3
//8
2**3
//8
-1<<3
//-8
-2**3
//
报错
-(2**3)
//-8
3<<2
//12
错误
3**2
//9
正确
是否是指定字符串开头：
!
和
^
!str1.indexOf("str2")
例：
var
str1='abc'
var
str2='a'
if(!str1.indexOf(str2)){
console.log('是开头')
}else{
console.log('不是开头')
}
使用正则方式
/^a/.test('abc')
//a开头，true
/c$/.test('abc')
//c结尾，true
字符串转数字：
+
+str
例：
var
str='123'
typeof(str)
//string
typeof(+str)
//number
转为
Boolean
值：
!!
!!obj
例：
!!'text'
//true
1、一个表达式中如果有减号 (-)、乘号 (*) 或 除号 (/) 等运算符时，JS 引擎在计算之前，会试图将表达式的每个分项转化为 Number 类型（使用 Number(x) 做转换）。如果转换失败，表达式将返回 NaN 。如果其中有一个变量是字符串，则会将两边都作为字符串相加。
2、一元加操作符也可以实现与 Number 相同的作用。
+'12abc'// NaN+'123'// 123
3、现在分析 'b'+'a'+ +'a'+'a'
上面的表达式相当于'b'+'a'+ (+'a')+'a'
因为(+'a') 等于 NaN，所以：
'b'+'a'+ (+'a')+'a' = 'b'+'a'+ "NaN"+'a'='baNaNa'
$(window).keydown(function(event){switch(event.keyCode) {
// ...
// 不同的按键可以做不同的事情
// 不同的浏览器的keycode不同
// 更多详细信息: http://unixpapa.com/js/key.html
// ...
}
})
keycode 0 =
keycode 1 =
keycode 2 =
keycode 3 =
keycode 4 =
keycode 5 =
keycode 6 =
keycode 7 =
keycode 8 = BackSpace BackSpace
keycode 9 = Tab Tab
keycode 10 =
keycode 11 =
keycode 12 = Clear
keycode 13 = Enter
keycode 14 =
keycode 15 =
keycode 16 = Shift_L
keycode 17 = Control_L
keycode 18 = Alt_L
keycode 19 = Pause
keycode 20 = Caps_Lock
keycode 21 =
keycode 22 =
keycode 23 =
keycode 24 =
keycode 25 =
keycode 26 =
keycode 27 = Escape Escape
keycode 28 =
keycode 29 =
keycode 30 =
keycode 31 =
keycode 32 = space space
keycode 33 = Prior
keycode 34 = Next
keycode 35 = End
keycode 36 = Home
keycode 37 = Left
keycode 38 = Up
keycode 39 = Right
keycode 40 = Down
keycode 41 = Select
keycode 42 = Print
keycode 43 = Execute
keycode 44 =
keycode 45 = Insert
keycode 46 = Delete
keycode 47 = Help
keycode 48 = 0 equal braceright
keycode 49 = 1 exclam onesuperior
keycode 50 = 2 quotedbl twosuperior
keycode 51 = 3 section threesuperior
keycode 52 = 4 dollar
keycode 53 = 5 percent
keycode 54 = 6 ampersand
keycode 55 = 7 slash braceleft
keycode 56 = 8 parenleft bracketleft
keycode 57 = 9 parenright bracketright
keycode 58 =
keycode 59 =
keycode 60 =
keycode 61 =
keycode 62 =
keycode 63 =
keycode 64 =
keycode 65 = a A
keycode 66 = b B
keycode 67 = c C
keycode 68 = d D
keycode 69 = e E EuroSign
keycode 70 = f F
keycode 71 = g G
keycode 72 = h H
keycode 73 = i I
keycode 74 = j J
keycode 75 = k K
keycode 76 = l L
keycode 77 = m M mu
keycode 78 = n N
keycode 79 = o O
keycode 80 = p P
keycode 81 = q Q at
keycode 82 = r R
keycode 83 = s S
keycode 84 = t T
keycode 85 = u U
keycode 86 = v V
keycode 87 = w W
keycode 88 = x X
keycode 89 = y Y
keycode 90 = z Z
keycode 91 =
keycode 92 =
keycode 93 =
keycode 94 =
keycode 95 =
keycode 96 = KP_0 KP_0
keycode 97 = KP_1 KP_1
keycode 98 = KP_2 KP_2
keycode 99 = KP_3 KP_3
keycode 100 = KP_4 KP_4
keycode 101 = KP_5 KP_5
keycode 102 = KP_6 KP_6
keycode 103 = KP_7 KP_7
keycode 104 = KP_8 KP_8
keycode 105 = KP_9 KP_9
keycode 106 = KP_Multiply KP_Multiply
keycode 107 = KP_Add KP_Add
keycode 108 = KP_Separator KP_Separator
keycode 109 = KP_Subtract KP_Subtract
keycode 110 = KP_Decimal KP_Decimal
keycode 111 = KP_Divide KP_Divide
keycode 112 = F1
keycode 113 = F2
keycode 114 = F3
keycode 115 = F4
keycode 116 = F5
keycode 117 = F6
keycode 118 = F7
keycode 119 = F8
keycode 120 = F9
keycode 121 = F10
keycode 122 = F11
keycode 123 = F12
keycode 124 = F13
keycode 125 = F14
keycode 126 = F15
keycode 127 = F16
keycode 128 = F17
keycode 129 = F18
keycode 130 = F19
keycode 131 = F20
keycode 132 = F21
keycode 133 = F22
keycode 134 = F23
keycode 135 = F24
keycode 136 = Num_Lock
keycode 137 = Scroll_Lock
keycode 138 =
keycode 139 =
keycode 140 =
keycode 141 =
keycode 142 =
keycode 143 =
keycode 144 =
keycode 145 =
keycode 146 =
keycode 147 =
keycode 148 =
keycode 149 =
keycode 150 =
keycode 151 =
keycode 152 =
keycode 153 =
keycode 154 =
keycode 155 =
keycode 156 =
keycode 157 =
keycode 158 =
keycode 159 =
keycode 160 =
keycode 161 =
keycode 162 =
keycode 163 =
keycode 164 =
keycode 165 =
keycode 166 =
keycode 167 =
keycode 168 =
keycode 169 =
keycode 170 =
keycode 171 =
keycode 172 =
keycode 173 =
keycode 174 =
keycode 175 =
keycode 176 =
keycode 177 =
keycode 178 =
keycode 179 =
keycode 180 =
keycode 181 =
keycode 182 =
keycode 183 =
keycode 184 =
keycode 185 =
keycode 186 =
keycode 187 = acute grave
keycode 188 = comma semicolon
keycode 189 = minus underscore
keycode 190 = period colon
keycode 191 =
keycode 192 = numbersign apostrophe
keycode 193 =
keycode 194 =
keycode 195 =
keycode 196 =
keycode 197 =
keycode 198 =
keycode 199 =
keycode 200 =
keycode 201 =
keycode 202 =
keycode 203 =
keycode 204 =
keycode 205 =
keycode 206 =
keycode 207 =
keycode 208 =
keycode 209 =
keycode 210 = plusminus hyphen macron
keycode 211 =
keycode 212 = copyright registered
keycode 213 = guillemotleft guillemotright
keycode 214 = masculine ordfeminine
keycode 215 = ae AE
keycode 216 = cent yen
keycode 217 = questiondown exclamdown
keycode 218 = onequarter onehalf threequarters
keycode 219 =
keycode 220 = less greater bar
keycode 221 = plus asterisk asciitilde
keycode 222 =
keycode 223 =
keycode 224 =
keycode 225 =
keycode 226 =
keycode 227 = multiply division
keycode 228 = acircumflex Acircumflex
keycode 229 = ecircumflex Ecircumflex
keycode 230 = icircumflex Icircumflex
keycode 231 = ocircumflex Ocircumflex
keycode 232 = ucircumflex Ucircumflex
keycode 233 = ntilde Ntilde
keycode 234 = yacute Yacute
keycode 235 = oslash Ooblique
keycode 236 = aring Aring
keycode 237 = ccedilla Ccedilla
keycode 238 = thorn THORN
keycode 239 = eth ETH
keycode 240 = diaeresis cedilla currency
keycode 241 = agrave Agrave atilde Atilde
keycode 242 = egrave Egrave
keycode 243 = igrave Igrave
keycode 244 = ograve Ograve otilde Otilde
keycode 245 = ugrave Ugrave
keycode 246 = adiaeresis Adiaeresis
keycode 247 = ediaeresis Ediaeresis
keycode 248 = idiaeresis Idiaeresis
keycode 249 = odiaeresis Odiaeresis
keycode 250 = udiaeresis Udiaeresis
keycode 251 = ssharp question backslash
keycode 252 = asciicircum degree
keycode 253 = 3 sterling
keycode 254 = Mode_switch
键代码
Backspace {BACKSPACE}、{BS} 或 {BKSP}
Break {BREAK}
Caps Lock {CAPSLOCK}
Del 或 Delete {DELETE} 或 {DEL}
向下键{DOWN}
End {END}
Enter {ENTER} 或 ~
Esc {ESC}
Help
{HELP}
Home
{HOME}
Ins 或 Insert
{INSERT} 或 {INS}
向左键
{LEFT}
Num Lock
{NUMLOCK}
Page Down
{PGDN}
Page Up
{PGUP}
Print Screen
{PRTSC}（保留供将来使用）
向右键
{RIGHT}
Scroll Lock
{SCROLLLOCK}
Tab
{TAB}
向上键
{UP}
F1
{F1}
F2
{F2}
F3
{F3}
F4
{F4}
F5
{F5}
F6
{F6}
F7
{F7}
F8
{F8}
F9
{F9}
F10
{F10}
F11
{F11}
F12
{F12}
F13
{F13}
F14
{F14}
F15
{F15}
F16
{F16}
数字键盘加号
{ADD}
数字键盘减号
{SUBTRACT}
数字键盘乘号
{MULTIPLY}
数字键盘除号
{DIVIDE}
若要指定与 Shift、Ctrl 和 Alt 键的任意组合一起使用的键，请在这些键代码之前加上以下一段或多段代码。
取余运算符 (%)
