无涯教程-Javascript

让无涯教程用一个简单的表达式 4 + 5=9 。这里的4和5称为操作数，" +"称为运算符，JavaScript支持以下类型的运算符。

算术运算符
比较运算符
逻辑运算符
赋值运算符
三元)运算符

算术运算符

JavaScript支持以下算术运算符，假设变量A=10，变量B=20，则:

Sr.No.	Operator & Description
1	+(加法) 两个数相加，如: A + B=30
2	-(减法) 第一个数减去第二个数，如: A-B=-10
3	(乘法) 两个数相乘，如: A B=200
4	/(除) 分子除以分母取整，如: B/A=2
5	％(取模) 相除后的余数，如: B％A=0
6	++(增量) 将整数值加1，如: A ++=11
7	-(递减) 将整数值减一，如: A--=9

注意 - 加法运算符(+)适用于数字和字符串。如" a" + 10将得到" a10"。

以下代码显示了如何在JavaScript中使用算术运算符。

<html><body><script type = "text/javascript"><!--var a = 33;var b = 10;var c = "Test";var linebreak = "<br />";document.write("a + b=");result = a + b;document.write(result);document.write(linebreak);document.write("a - b=");result = a - b;document.write(result);document.write(linebreak);document.write("a/b=");result = a/b;document.write(result);document.write(linebreak);document.write("a % b=");result = a % b;document.write(result);document.write(linebreak);document.write("a + b + c=");result = a + b + c;document.write(result);document.write(linebreak);a = ++a;document.write("++a=");result = ++a;document.write(result);document.write(linebreak);b = --b;document.write("--b=");result = --b;document.write(result);document.write(linebreak);//--></script>Set the variables to different values and then try...</body>
</html>

运行上面代码输出

a + b=43
a - b=23
a/b=3.3
a % b=3
a + b + c=43
++a=35
--b=8
Set the variables to different values and then try...

比较运算符

JavaScript支持以下比较运算符，假设变量A=10，变量B=20，则:

Sr.No.	Operator & Description
1	==(等于) 检查两个值是否相等，如 :(A == B)=false。
2	!=(不等于) 检查两个值是否不相等，如:(A!= B)=true。
3	> (大于) 检查左数的值是否大于右数的值，如: (A > B)=false
4	< (小于) 检查左数的值是否小于右数的值，如: (A < B)=true.
5	>= (大于或等于) 检查左操作数的值是否大于或等于右操作数的值，如: (A >= B)=false.
6	<= (小于或等于) 检查左操作数的值是否小于或等于右操作数的值，如: (A <= B)=true

以下代码显示了如何在JavaScript中使用比较运算符。

<html><body>  <script type = "text/javascript"><!--var a = 10;var b = 20;var linebreak = "<br />";document.write("(a == b) => ");result = (a == b);document.write(result);document.write(linebreak);document.write("(a < b) => ");result = (a < b);document.write(result);document.write(linebreak);document.write("(a > b) => ");result = (a > b);document.write(result);document.write(linebreak);document.write("(a != b) => ");result = (a != b);document.write(result);document.write(linebreak);document.write("(a >= b) => ");result = (a >= b);document.write(result);document.write(linebreak);document.write("(a <= b) => ");result = (a <= b);document.write(result);document.write(linebreak);//--></script>      Set the variables to different values and different operators and then try...</body>
</html>

运行上面代码输出

(a == b) => false 
(a < b) => true 
(a > b) => false 
(a != b) => true 
(a >= b) => false 
a <= b) => true
Set the variables to different values and different operators and then try...

逻辑运算符

JavaScript支持以下逻辑运算符，假设变量A=10，变量B=20，则:

Sr.No.	Operator & Description
1	&& (AND) 如果两个数都不为零，则返回为true。如: (A && B)=true.
2	\|\| (OR) 如果两个数中的任何一个都不为零，则返回true。如:(A \|\| B)=true。
3	!(NOT) 反转其操作数的逻辑状态，如果条件为true，则返回false。如: ! (A && B)=false.

Sr.No.

Operator & Description

&& (AND)

如果两个数都不为零，则返回为true。如: (A && B)=true.

|| (OR)

如果两个数中的任何一个都不为零，则返回true。如:(A || B)=true。

!(NOT)

反转其操作数的逻辑状态，如果条件为true，则返回false。如: ! (A && B)=false.

尝试以下代码，以了解如何在JavaScript中实现逻辑运算符。

<html><body>   <script type = "text/javascript"><!--var a = true;var b = false;var linebreak = "<br />";document.write("(a && b) => ");result = (a && b);document.write(result);document.write(linebreak);document.write("(a || b) => ");result = (a || b);document.write(result);document.write(linebreak);document.write("!(a && b) => ");result = (!(a && b));document.write(result);document.write(linebreak);//--></script>      <p>Set the variables to different values and different operators and then try...</p></body>
</html>

运行上面代码输出

(a && b) => false 
(a || b) => true 
!(a && b) => true
Set the variables to different values and different operators and then try...

按位运算符

JavaScript支持以下按位运算符，假设变量A=2，变量B=3，则:

Sr.No.	Operator & Description
1	& ( AND) 对其整数参数的每一位执行布尔"AND"运算。如: (A & B) = 2.
2	\| (OR) 对其整数参数的每一位执行布尔"OR"运算。如:(A \| B) = 3。
3	^(XOR) 对其整数参数的每一位执行布尔异或(^)运算。如:(A ^ B)=1。
4	〜(NOT) 一元运算符，通过反转操作数中的所有位进行操作。如:(〜B)=-4。
5	<< (左移) 将值左移一个位置等同于将其乘以2，将两个位置左移等同于乘以4，新位填充零。如: (A << 1) = 4.
6	>> (右移) 与左移相反，右移一位相等于除以2。如: (A >> 1)=1.
7	>>> (右移零) 该运算符类似于>>运算符，不同之处在于向左移的位始终为零。如: (A >>> 1)=1.

尝试使用以下代码在JavaScript中实现按位运算符。

<html><body>   <script type = "text/javascript"><!--var a = 2; //Bit presentation 10var b = 3; //Bit presentation 11var linebreak = "<br />";document.write("(a & b) => ");result = (a & b);document.write(result);document.write(linebreak);document.write("(a | b) => ");result = (a | b);document.write(result);document.write(linebreak);document.write("(a ^ b) => ");result = (a ^ b);document.write(result);document.write(linebreak);document.write("(~b) => ");result = (~b);document.write(result);document.write(linebreak);document.write("(a << b) => ");result = (a << b);document.write(result);document.write(linebreak);document.write("(a >> b) => ");result = (a >> b);document.write(result);document.write(linebreak);//--></script>      <p>Set the variables to different values and different operators and then try...</p></body>
</html>

运行上面代码输出

(a & b) => 2 
(a | b) => 3 
(a ^ b) => 1 
(~b) => -4 
(a << b) => 16 
(a >> b) => 0
Set the variables to different values and different operators and then try...

赋值运算符

JavaScript支持以下赋值运算符:

Sr.No.	Operator & Description
1	=(赋值) 将值从右侧操作数分配到左侧操作数。如: C=A + B 等于将A + B的值赋给C
2	+=(添加和赋值) 将右操作数添加到左操作数，并将输出分配给左操作数。如 : C +=A 等于 C=C + A
3	-=(减法和赋值) 从左侧操作数中减去右侧操作数，并将输出分配给左侧操作数。如: C-= A 等于 C=C-A
4	= (乘法和赋值) 将右操作数与左操作数相乘，并将输出分配给左操作数。如: C =A 等于 C=C * A
5	/=(相除和赋值) 将左操作数除以右操作数，并将输出分配给左操作数。如: C/= A 等于 C=C/A
6	％=(取模和赋值) 使用两个操作数取模，并将输出分配给左操作数。如 : C％= A等于C=C％A

尝试以下代码在JavaScript中实现赋值运算符。

<html><body>   <script type = "text/javascript"><!--var a = 33;var b = 10;var linebreak = "<br />";document.write("Value of a => (a=b) => ");result = (a = b);document.write(result);document.write(linebreak);document.write("Value of a => (a += b) => ");result = (a += b);document.write(result);document.write(linebreak);document.write("Value of a => (a -= b) => ");result = (a -= b);document.write(result);document.write(linebreak);document.write("Value of a => (a *= b) => ");result = (a *= b);document.write(result);document.write(linebreak);document.write("Value of a => (a /= b) => ");result = (a /= b);document.write(result);document.write(linebreak);document.write("Value of a => (a %= b) => ");result = (a %= b);document.write(result);document.write(linebreak);//--></script>      <p>Set the variables to different values and different operators and then try...</p></body>
</html>

运行上面代码输出

Value of a => (a=b) => 10
Value of a => (a += b) => 20 
Value of a => (a -= b) => 10 
Value of a => (a *= b) => 100 
Value of a => (a /= b) => 10
Value of a => (a %= b) => 0
Set the variables to different values and different operators and then try...

条件运算符(?:)

条件运算符首先对表达式的真值或假值求值，然后根据求值输出执行两个给定语句之一。

NO	描述
1	? :(三元运算符) eg: x==2?X:Y; 如果x==2，则返回X，否则返回Y

请尝试以下代码，以了解条件运算符在JavaScript中的工作方式。

<html><body>   <script type = "text/javascript"><!--var a = 10;var b = 20;var linebreak = "<br />";document.write ("((a > b) ? 100 : 200) => ");result = (a > b) ? 100 : 200;document.write(result);document.write(linebreak);document.write ("((a < b) ? 100 : 200) => ");result = (a < b) ? 100 : 200;document.write(result);document.write(linebreak);//--></script>      <p>Set the variables to different values and different operators and then try...</p></body>
</html>

运行上面代码输出

((a > b) ? 100 : 200) => 200 
((a < b) ? 100 : 200) => 100
Set the variables to different values and different operators and then try...

类型运算符

typeof 运算符是一元运算符，位于其单个操作数的前面，该操作数可以是任何类型。它的值是一个字符串，指示操作数的数据类型。

这是 typeof 运算符的返回值列表。

类型	由typeof返回的字符串
Number	"number"
String	"string"
Boolean	"boolean"
Object	"object"
Function	"function"
Undefined	"undefined"
Null	"object"

以下代码显示了如何实现 typeof 运算符。

<html><body>      <script type = "text/javascript"><!--var a = 10;var b = "String";var linebreak = "<br />";result = (typeof b == "string" ? "B is String" : "B is Numeric");document.write("Result => ");document.write(result);document.write(linebreak);result = (typeof a == "string" ? "A is String" : "A is Numeric");document.write("Result => ");document.write(result);document.write(linebreak);//--></script>      <p>Set the variables to different values and different operators and then try...</p></body>
</html>

运行上面代码输出

Result => B is String 
Result => A is Numeric
Set the variables to different values and different operators and then try...

参考链接

https://www.learnfk.com/javascript/javascript-operators.html