算术运算符
| Operator | Description | Example | Result |
|---|---|---|---|
| + | Addition
加 |
x=2
y=2 x+y |
4 |
| - | Subtraction
减 |
x=5
y=2 x-y |
3 |
| * | Multiplication
乘 |
x=5
y=4 x*y |
20 |
| / | Division
除 |
15/5
5/2 |
3
2.5 |
| % | Modulus (division remainder)
余数 |
5%2
10%8 10%2 |
1
2 0 |
| ++ | Increment
递增 |
x=5
x++ |
x=6 |
| -- | Decrement
递减 |
x=5
x-- |
x=4 |
赋值运算符
| Operator | Example | Is The Same As |
|---|---|---|
| = | x=y | x=y |
| += | x+=y | x=x+y |
| -= | x-=y | x=x-y |
| *= | x*=y | x=x*y |
| /= | x/=y | x=x/y |
| %= | x%=y | x=x%y |
比较（关系）运算符
| Operator | Description | Example |
|---|---|---|
| == | is equal to
等于 |
5==8 returns false |
| === | is equal to (checks for both value and type)
等于（检查值和类型）*全吻合才算相等 |
x=5
y="5" x==y returns true x===y returns false |
| != | is not equal
不等于 |
5!=8 returns true |
| > | is greater than
大于 |
5>8 returns false |
| < | is less than
小于 |
5<8 returns true |
| >= | is greater than or equal to
大于等于 |
5>=8 returns false |
| <= | is less than or equal to
小于等于 |
5<=8 returns true |
逻辑运算符
| Operator | Description | Example |
|---|---|---|
| && | and
与 |
x=6
y=3 (x < 10 && y > 1) returns true |
| || | or
或 |
x=6
y=3 (x==5 || y==5) returns false |
| ! | not
非 |
x=6
y=3 !(x==y) returns true |
串符（连接作用）
A string is most often text, for example "Hello World!". To stick two or more string variables together, use the + operator.
在文字当中使用的比较多，举例来说“Hello World!”要将两个或多个字符串变量衔接在一起的话就得使用 + 符号
txt1="What a very" txt2="nice day!" txt3=txt1+txt2 |
The variable txt3 now contains "What a verynice day!".
txt3变量现在包含“What a verynice day!”（把1和2衔接起来了）
To add a space between two string variables, insert a space into the expression, OR in one of the strings.
要给两个字符串变量中间添加空格就得在表达式里插入空格，或在其中的一个加上（空格）
txt1="What a very" txt2="nice day!" txt3=txt1+" "+txt2 or txt1="What a very " txt2="nice day!" txt3=txt1+txt2 |
The variable txt3 now contains "What a very nice day!".
现在变量txt3为“What a very nice day!”
条件运算符
JavaScript also contains a conditional operator that assigns a value to a variable based on some condition.
JS有根据条件不同给变量不同值的条件运算符
语法
variablename=(condition)?value1:value2 |
例子
greeting=(visitor=="PRES")?"Dear President ":"Dear " |
If the variable visitor is equal to PRES, then put the string "Dear President " in the variable named greeting. If the variable visitor is not equal to PRES, then put the string "Dear " into the variable named greeting.
如果变量visitor的值等于PRES那么greeting的值就为"Dear President "。如果不为PRES那么greeting的值就为"Dear"