JS 操作符整理[推薦收藏]

Arithmetic Operators
算術運算子

Operator	Description	Example	Result
+	Addition 加	x=2 y=2 x+y	4
-	Subtraction 減	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) 餘數	5%2 10%8 10%2	1 2 0
++	Increment 遞增	x=5 x++	x=6
--	Decrement 遞減	x=5 x--	x=4

Assignment Operators
賦值運算子

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

Comparison Operators
比較（關係）運算子

Operator	Description	Example
==	is equal to 等於	5==8 returns false
===	is equal to (checks for both value and type) 等於（檢查值和類型）*全吻合才算相等	x=5 y="5" x==y returns true x===y returns false
!=	is not equal 不等於	5!=8 returns true
>	is greater than 大於	5>8 returns false
<	is less than 小於	5<8 returns true
>=	is greater than or equal to 大於等於	5>=8 returns false
<=	is less than or equal to 小於等於	5<=8 returns true

Logical Operators
邏輯運算子

Operator	Description	Example
&&	and 與	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

String Operator
串符（串連作用）

A string is most often text, for example "Hello World!". To stick two or more string variables together, use the + operator.
在文字當中使用的比較多，舉例來說“Hello World!”要將兩個或多個字串變數銜接在一起的話就得使用 + 符號

txt1="What a very"txt2="nice day!"txt3=txt1+txt2

The variable txt3 now contains "What a verynice day!".
txt3變數現在包含“What a verynice day!”（把1和2銜接起來了）

To add a space between two string variables, insert a space into the expression, OR in one of the strings.
要給兩個字串變數中間添加空格就得在運算式裡插入空格，或在其中的一個加上（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!".
現在變數txt3為“What a very nice day!”

Conditional Operator
條件運算子

JavaScript also contains a conditional operator that assigns a value to a variable based on some condition.
JS有根據條件不同給變數不同值的條件運算子

Syntax
文法

variablename=(condition)?value1:value2

Example
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.
如果變數visitor的值等於PRES那麼greeting的值就為"Dear President "。如果不為PRES那麼greeting的值就為"Dear"