javascript type conversion.

Directory:
1: Pseudo object
2: Convert to string
3: Convert number to string
4: Convert to number
5: Convert to Boolean
6: The difference between Number() and parseInt()
7: String The difference between () and toString()

1: Pseudo-object
Pseudo-object: JavaScript is a very interesting language. Even basic types are pseudo-objects, so they all have properties and methods.
The type of variable a is a string, and its length can be obtained by calling its property length, which is a pseudo object.

<script><br/> var a="hello javascript"; <br/> document.write("变量a的类型是:"+(typeof a));<br/> document.write("<br>");<br/> document.write("变量a的长度是:"+a.length);<br/></script>

Operation effect:
The type of variable a is: string
The length of variable a is: 16

2: Convert to string
Whether it is Number, Boolean or String, there is a toString method for converting to String

<script><br/> var a=10; <br/> document.write("数字 "+a+" 转换为字符串"+a.toString());<br/> document.write("<br>");<br/><br/> var b=true; <br/> document.write("布尔 "+b+" 转换为字符串"+b.toString());<br/> document.write("<br>");<br/><br/> var c="hello javascript"; <br/> document.write("字符串 "+c+" 转换为字符串 "+c.toString());<br/> document.write("<br>");<br/><br/></script>

Operation effect:
Number 10 is converted to string 10
Boolean true is converted to string true
String hello javascript is converted to string hello javascript

3: Number to string
Number is converted to character When stringing, there are two types: default mode and base mode
<script><br/> var a=10; <br/> document.write(&#39;默认模式下，数字10转换为十进制的&#39;+a.toString()); //默认模式，即十进制<br/> document.write("<br>"); <br/><br/> document.write(&#39;基模式下，数字10转换为二进制的&#39;+a.toString(2)); //基模式，二进制<br/> document.write("<br>"); <br/> <br/> document.write(&#39;基模式下，数字10转换为八进制的&#39;+a.toString(8)); //基模式，八进制<br/> document.write("<br>"); <br/><br/> document.write(&#39;基模式下，数字10转换为十六进制的&#39;+a.toString(16)); //基模式，十六进制<br/> document.write("<br>"); <br/><br/></script>
Operating effect:
In default mode, the number 10 is converted to decimal 10
In base mode, the number 10 is converted to binary 1010
In base mode, the number 10 is converted to In the octal 12
base mode, the number 10 is converted to hexadecimal a

4: converted to a number
Javascript provides built-in functions parseInt() and parseFloat() respectively to convert to a number

Note: If it is converted A string is composed of numbers and characters at the same time, so parseInt will keep positioning numbers until non-characters appear. So "10abc" will be converted to 10

Question: What will the string "10abc8" be converted to?

<script><br/> document.write("字符串的\"10\"转换为数字的:"+parseInt("10")); //转换整数<br/> document.write("<br>");<br/> document.write("字符串的\"3.14\"转换为数字的:"+parseFloat("444 3.14"));//转换浮点数<br/> document.write("<br>");<br/> document.write("字符串的\"10abc\"转换为数字的:"+parseInt("10abc")); //判断每一位，直到发现不是数字的那一位<br/> document.write("<br>");<br/><br/> document.write("字符串的\"hello javascript\"转换为数字的:"+parseInt("h5555ello javascript")); //如果完全不包含数字，则返<br/><br/>回NaN - Not a Number<br/> document.write("<br>");<br/><br/></script>
Operation effect:
The string "10" is converted to a number: 10
The string "3.14" is converted to a number: 444
The string "10abc" is converted to a number: 10
The string "hello javascript" converted to a number: NaN

5: converted to Boolean
Use the built-in function Boolean() to convert to a Boolean value
When converting a string:
Non-empty means true
When converting a number:
Not 0 That is true
When converting the object:
Non-null is true

<script><br/> document.write("空字符串&#39;&#39;转换为布尔后的值:"+Boolean("")); //空字符串<br/> document.write("<br>");<br/> document.write("非空字符&#39;hello javascript &#39;串转换为布尔后的值:"+Boolean("hello javascript")); //非空字符串<br/> document.write("<br>");<br/> document.write("数字 0 转换为布尔后的值:"+Boolean(0)); //0<br/> document.write("<br>");<br/> document.write("数字 3.14 转换为布尔后的值:"+Boolean(3.14)); //非0 <br/> document.write("<br>");<br/> document.write("空对象 null 转换为布尔后的值:"+Boolean(null)); //null<br/> document.write("<br>");<br/> document.write("非对象 new Object() 转换为布尔后的值:"+Boolean(new Object())); //对象存在<br/> document.write("<br>");<br/></script>

Operating effect:
The value after converting the empty string '' to Boolean: false
After the non-empty character 'hello javascript ' string is converted to Boolean Value: true
Number 0 Value after conversion to Boolean: false
Number 3.14 Value after conversion to Boolean: true
Empty object null Value after conversion to Boolean: false
Non-object new Object() Conversion to Boolean Value: true

6: The difference between Number() and parseInt()
Number(), like parseInt(), can be used to convert numbers
The difference is that when the converted content contains non-numbers, Number( ) will return NaN (Not a Number)
parseInt() It depends on the situation. If it starts with a number, it will return the legal number part at the beginning. If it starts with a non-number, it will return NaN

<script><br/> document.write("通过Number() 函数转换字符串&#39;123&#39; 后得到的数字："+Number("123")); //正常的<br/> document.write("<br>");<br/> document.write("通过Number() 函数转换字符串&#39;123abc&#39; 后得到的数字："+Number("123abc")); //包含非数字<br/> document.write("<br>");<br/> document.write("通过Number() 函数转换字符串&#39;abc123&#39; 后得到的数字："+Number("abc123")); //包含非数字<br/> document.write("<br>");<br/><br/> document.write("通过parseInt() 函数转换字符串&#39;123&#39; 后得到的数字："+parseInt("123")); //正常的<br/> document.write("<br>");<br/> document.write("通过parseInt() 函数转换字符串&#39;123abc&#39; 后得到的数字："+parseInt("123abc")); //包含非数字,返回开头的合法<br/><br/>数字部分<br/> document.write("<br>");<br/> document.write("通过parseInt() 函数转换字符串&#39;abc123&#39; 后得到的数字："+parseInt("abc123")); //包含非数字,以非数字开头，<br/><br/>返回NaN<br/> document.write("<br>");<br/><br/></script>

Operation effect:
Passed The number obtained after converting the string '123' with the Number() function: 123
The number obtained after converting the string '123abc' with the Number() function: NaN
The number obtained after converting the string 'abc123' with the Number() function : NaN
The number obtained after converting the string '123' through the parseInt() function: 123
The number obtained after converting the string '123abc' through the parseInt() function: 123
Converting the string 'abc123' through the parseInt() function The number obtained after: NaN

7: The difference between String() and toString()
String() and toString() both return strings, the difference lies in the processing of null
String() will return the string "null"
toString() will report an error and cannot be executed

<script><br/> var a = null;<br/> document.write(&#39;String(null) 把空对象转换为字符串：&#39;+String(a)); <br/> document.write("<br>"); <br/> document.write(&#39;null.toString() 就会报错，所以后面的代码不能执行&#39;); <br/> document.write(a.toString()); <br/> document.write("因为第5行报错，所以这一段文字不会显示"); <br/></script>

Operating effect:
String(null) Convert the empty object to a string: null
null.toString() will report an error, so the following code cannot be executed

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