Summary of the eight types of operators in JavaScript

1. Unary operator

1. delete operator: deletes references to previously defined object properties or methods. For example:

var o=new Object; 
o.name="superman"; 
alert(o.name); //输出 "superman" 
delete o.name; 
alert(o.name); //输出 "undefined"

Remove the name attribute and set it to undefined (that is, the value of the uninitialized variable created). delete cannot delete properties and methods that are not defined by the developer (that is, defined by ECMAScript).
For example, the following code will cause an error: delete o.toString();

2. void operator: Returns undefined for any value. This operator is typically used to avoid outputting values ​​that should not be output.
For example: in the HTML page Click Me
Click the link, the link in the webpage disappears, and the display "[object]" (in IE, "[object Window]" is displayed in Firefox, and the link is still the same in Google). Because the window.open() method returns a reference to the newly opened window. The object is then converted into a string to be displayed. To avoid this result, you can use the void operator to call the window.open() function:

<a href="javascript:void(window.open(&#39;about:blank&#39;))">Click Me</a>

This causes the window.open() call to return undefined, which is not a valid value and will not be displayed in the browser in the browser window.

3. Pre-increment/pre-decrement operator: The usage is the same as in C. Operations occur before expressions are evaluated. Such as: ++i; --i.

4. Post-increment/post-decrement operator: Postfix operators perform increment or decrement operations after calculating the expressions containing them. Such as: i++; i--.

5. One-yuan addition and one-yuan subtraction
One-yuan addition essentially has no effect on numbers: var iNum=25; iNum=+iNum; alert(iNum); //Output 25
One-yuan addition When the operator operates on a string, the way it calculates the string is similar to parseInt(). The main difference is that for strings starting with "0x" (representing hexadecimal numbers), unary operators can Convert to decimal value. Therefore, converting "010" using unary addition will always result in 10, while "0xB" will be converted to 11.
var sNum="25"; alert(typeof sNum); //Output "string"
var iNum=+sNum; alert(typeof iNum); //Output "number"
Uniary subtraction is the right Negate a numerical value. Similar to the unary addition operator, the unary subtraction operator will also convert a string into an approximate number and will also negate the value.
var sNum = "25"; alert(typeof sNum); //Output "string"
var iNum = -sNum; alert(iNum); //Output "-25"
alert(typeof iNum ); //Output "number"

2. Bit operators: a series of operators related to binary
The bit operator NOT consists of the negation sign (~) express.
The bit operator AND is represented by the ampersand (&).
The bitwise operator OR is represented by the symbol (|).
The bitwise operator XOR is represented by the symbol (^).
The left shift operation is represented by two less than signs (<<).
The signed right shift operator is represented by two greater than signs (>>).
Unsigned right shift is represented by three greater than signs (>>>).

3. Boolean operators
There are three types of Boolean operators, namely NOT, AND and OR.
1. Logical NOT, represented by an exclamation point (!). This operator is typically used to control loops. Unlike the logical OR and logical AND operators, the logical NOT operator must return a Boolean value. The behavior of the logical NOT operator is as follows:
If the operand is an object, return false.
If the operand is the number 0, return true.
If the operand is any number other than 0, return false.
If the operand is null, return true.
If the operand is NaN, return true.
If the operand is undefined, an error occurs.
Example: var b = true;
while(!b){……}
2. Logical AND operator, represented by double ampersand (&&). There is only one situation when the result is true: true && true = true;
The operand of the logical AND operation can be of any type, not just Boolean values. If an operand is not a primitive Boolean value, the logical AND operation does not necessarily return a Boolean value:
If one operand is an object and the other is a Boolean value, return the object.
If both operands are objects, return the second object.
If an operand is null, return null.
If an operand is NaN, return NaN.
If an operand is undefined, an error occurs.
If the first operand is false, then no matter what the value of the second operand is, the result cannot be true.
3. Logical OR operator, represented by double vertical bars (||). There is only one case where the result is false: false || false=false; other cases are true.
Similar to the logical AND operator, if an operand is not a Boolean value, the logical OR operation does not necessarily return a Boolean value:
If one operand is an object and the other is a Boolean value, the object is returned.
If both operands are objects, return the first object.
If an operand is null, return null.
If an operand is NaN, return NaN.
If an operand is undefined, an error occurs.
Logical OR is also a simple operation. For the logical OR operator, if the first operand value is true, the second operand will not be calculated.

4. Multiplicative operator
1. The multiplication operator, represented by an asterisk (*), is used to multiply two numbers. But when dealing with special values, multiplication in ECMAScript also has some special behaviors:
If the operands are all numbers, perform regular multiplication operations. If the result is too large or too small, the generated result is Infinity or -Infinity. .
If an operand is NaN, the result is NaN.
Infinity multiplied by 0, the result is NaN.
Infinity multiplied by any number other than 0, the result is Infinity or -Infinity, determined by the sign of the second operand.
2. The division operator, represented by a slash (/), divides the first number by the second number. For special values, the special behavior is as follows:
If the operands are all numbers, perform regular trigger operations. If the result is too large or too small, the generated result is Infinity or -Infinity.
If an operand is NaN, the result is NaN.
0 divides a non-infinity number, the result is NaN.
Infinity is divided by any number other than 0, and the result is Infinity or -Infinity, determined by the sign of the second operand.
3. Modulo operator, expressed with percent sign (%). If the operands are both numbers, perform regular arithmetic division and return the remainder. Special behavior:
If the dividend is Infinity, or the divisor is 0, the result is NaN.
If the divisor is an infinite number, the result is the dividend.
If the dividend is 0, the result is 0.

5. Additive operator
1. Addition operator (+), special behavior:
A certain operand is NaN, and the result is NaN.
Infinity Add -Infinity, the result is NaN.
If an operand is a string, then the following rules apply:
If both operands are strings, concatenate the second string to the first string.
If only one operand is a string, convert the other operand into a string, and the result is a string concatenated by the two strings.
2. Subtraction operator (-), if both operands are numbers, arithmetic subtraction will be performed. Special rules:
If the operand is NaN, the result is NaN.
An operand is not a number, and the result is NaN.

六、关系运算符
关系运算符小于、大于、小于等于和大于等于执行的是两个数的比较运算，比较方式与算术比较运算相同。每个关系运算符都返回一个Boolean值。
对于字符串，第一个字符串中每个字符的代码都会与第二个字符串中对应位置上的字符的代码进行数值比较。
1、大写字母的代码都小于小写字母的代码，所以要得到按照真正的字母顺序比较结果，必须把两个运算数转换成相同的大小写形式，再进行比较。
2、在比较两个字符串形式的数字时，比较的是它们的字符代码。
3、比较一个字符串和数字，ECMAScript都会把字符串转换为数字，然后按照数字顺序比较它们。如果字符串不能转换成数字，那么返回NaN，任何包含NaN的关系运算都要返回false。因此，这样会返回false。

七、等性运算符

1、等号(==) 和非等号(!=)，为确定两个运算数是否相等，这两个运算符都会进行类型转换。执行类型转换的基本规则如下：
如果一个运算数是Boolean值，在检查相等性之前，把它转换成数字值。False转换成0，true转换成1。
如果一个运算数是字符串，另一个是数字，在检查相等性之前，要尝试把字符串转换成数字。
如果一个运算数是对象，另一个是字符串，在检查等性之前，要尝试把对象转换成字符串(调用toString()方法)。
如果一个运算数是对象，另一个是数字，在检查等性之前，要尝试把对象转换成数字。
在进行比较时，该运算符还遵守下列规则：
值null和undefined相等。
在检查相等性时，不能把null和undefined转换成其他值。
如果某个运算数是NaN，等号将返回false，非等号将返回true。即使两个运算数都是NaN，等号仍然返回false，因为根据规则，NaN不等于NaN。
如果两个运算数都是对象，那么比较的是他们的引用值。如果两个运算数指向同一个对象，那么等号返回true，否则两个运算数不等。

2、全等号和非全等号
等号和非等号的同类运算符是全等号和非全等号。这两个运算符所做的与等号和非等号相同，只是他们在检查相等性前，不执行类型转换。
全等号由三个等号(===)表示，只有在无需类型转换运算数就相等的情况下，才返回true。

var sNum="55"; var iNum=55; alert(sNum==iNum); //输出 "true" 
alert(sNum===iNum); //输出 "false"

非全等号由两个感叹号加两个等号(!==)表示，只有在无需类型转换运算数不相等的情况下，才返回true。

var sNum="55"; var iNum=55; alert(sNum != iNum); //输出 "false" 
alert(sNum !== iNum); //输出 "true"

八、其他运算符
1、条件运算符，即三元运算符 ： variable = boolean_expression ? true_value : false_value;
2、赋值运算符(=) 复合赋值运算符：+=、-=、*=、/=、%=、<<=、>>=、>>>=
3、逗号运算符 用逗号运算符可以在一条语句中执行多个运算。 如： var iNum1=1,iNum2=2;

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