Arithmetic Operators算术运算符 Operator Description Example Result + Addition 加 x=2y=2x+y 4 - Subtraction 减 x=5y=2x-y 3 * Multiplication 乘 x=5y=4x*y 20 / Division 除 15/55/2 32.5 % Modulus (division remainder) 余数 5%210%810%2 120 ++ Increment递增 x=5x++ x=6 -- Decrement递减 x=5x-- x=4 Assignment Operators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 Comparison Operators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=5y="5" x==y returns truex===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 Logical Operators逻辑运算符 Operator Description Example && and 与 x=6y=3 (x < 10 && y > 1) returns true || or 或 x=6y=3 (x==5 || y==5) returns false ! not 非 x=6y=3 !(x==y) returns true String Operator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+" "+txt2ortxt1="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!” Conditional Operator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 Syntax语法 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"

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