Detailed explanation of the use of the most basic regular expressions in JS

This time I will bring you the most basicregular expressions in JSDetailed explanation of usage, what are theprecautionsfor using basic regular expressions in JS, the following are practical cases , let’s take a look.

Regular expressions are a very powerful thing. Today I will just briefly introduce them to those who are new to JS. If there are any controversial aspects, please leave a message!

1.1 What is a regular expression

A regular expression is an object that describes a character pattern. ECMAScript The RegExp class represents regular expressions, and both String and RegExp define functions for powerful pattern matching and text retrieval and replacement using regular expressions.

Regular expressions are used to match string patterns and retrieve and replace them. They are a powerful tool for performing pattern matching on strings.

1.2 The role of regular expressions

Regular expressions are mainly used to verify the input data of the client.

After the user fills out the form and clicks the button, the form will be sent to the server. On the server side, server scripts such as PHP, ASP.NET, and JSP are usually used for further processing. Because of client-side verification, it can save a lot of server-side system resources and provide a better user experience.

2. Create a regular expression==(123)==

To use a regular expression, you must first create aregular expression Expression object, there are 2ways to create an object:

2.1 Method 1: Use the keyword new to create

var patt = new RegExp(pattern,modifiers);

parameters 1: Regular expression pattern. String form

Parameter 2: Mode modifier. Used to specify global matching, case-sensitive matching and multi-line matching

2.2 Method 2: Use regular expressions to directly quantify

var pa = /pattern/modifiers;

Two/middle ones Represents the pattern of a regular expression. The last / is followed by the pattern modifier

. For example: the above example can be written like this: var pa = /girl/gi;

Note: At this time, the pattern and Pattern modifiers can be added with double quotes or single quotes

3. Regular expression pattern modifiers==(126)==

There are three mode modifiers in JavaScript: g i u

1. g: indicates global. This means that a string will be matched multiple times. If g is not written, it will only be matched once. Once the match is successful, it will not be matched again.

2. i: Indicates that case is ignored. This means that the matching is not case-sensitive.

3. u: Indicates that multiple lines can be matched.

4. Detailed explanation of regular expression methods==(127)==

Frequently used regular expressions There are two test() and exec() methods

4.1 test() method

test(string)

• Parameter: The string to be matched

• Return value: Return true if the match is successful, false if failed

If you only want to know the target character This method is very convenient when you don't need to know whether a string matches a certain pattern, but you don't need to know its text content. Therefore, the test() method is often used in if statements.

4.2 exec() method

exec(string): This method is specially designed for capturing groups

• Parameter: The string to be matched

• Return value: An array is returned. If there is no match, return null

• Explanation about the return value array:

• It is indeed an instance of Array.

• But this array has two additional attributes: index and input

• index: indicates where the matched string is in the source string Index

• #input: Indicates the matched source string.

• 数组的第一项目是与整个模式匹配的字符串，其他项是与模式中捕获组匹配的字符串

• 如果没有捕获组，则数组中只有第一项。关于捕获组的概念以后再说

所以我们如果想找到全部匹配的字符串可以时候用循环，结束条件就是匹配结果为null

分组。在正则表达式中用()括起来任务是一组。组可以嵌套。

 //最终运行结果： girlGirl Girl ------------- Girlgirl girl ------------

五、正则表达式规则==(124)==

表达式规则

正则表达式元字符是包含特殊含义的字符。它们有一些特殊功能，可以控制匹配模式的

方式。反斜杠后的元字符将失去其特殊含义。

字符类：单个字符和数字

[0-9A-Za-z]
元字符/元符号 匹配情况
. 匹配除换行符外的任意字符
[a-z0-9] 匹配括号中的字符集中的任意字符
[^a-z0-9] 匹配任意不在括号中的字符集中的字符
\d ==[0-9] 匹配数字
\D ==[^0-9] 匹配非数字，同[^0-9]相同
\w [0-9A-Za-z_] 匹配字母和数字及_
\W 匹配非(字母和数字及_)

字符类：空白字符
元字符/元符号 匹配情况
\0 匹配null 字符
\b 匹配空格字符
\n 匹配换行符
\r 匹配回车字符
\t 匹配制表符
\s 匹配空白字符、空格、制表符和换行符
\S 匹配非空白字符

字符类：锚字符

元字符/元符号 匹配情况
^ 行首匹配
$ 行尾匹配

字符类：重复字符
元字符/元符号 匹配情况
? 例如（x?） 匹配0个或1 个x
* 例如（x*） 匹配0个或任意多个x
+ 例如（x+） 匹配至少一个x
(xyz)+ 匹配至少一个(xyz)
{m,n} 例如x{m,n} n>=次数>=m 匹配最少m个、最多n个x
{n} 匹配前一项n次
{n,} 匹配前一项n次，或者多次

六、常用正则表示==(128)==

1、检查邮政编码

var pattern = /[1-9][0-9]{5}/; //共6位数字，第一位不能为0 var str = '224000'; alert(pattern.test(str));

2、检查文件压缩包

var pattern = /[\w]+\.zip|rar|gz/; //\w 表示所有数字和字母加下划线 var str = '123.zip'; //\.表示匹配.，后面是一个选择 alert(pattern.test(str));

3、删除多余空格

var pattern = /\s/g; //g 必须全局，才能全部匹配 var reg=new RegExp('\\s+','g'); var str = '111 222 333'; var result = str.replace(pattern,''); //把空格匹配成无空格 alert(result);

4、删除空格

var pattern = /^\s+/; var str = ' goo gle '; alert(str+" "+str.length); var result = str.replace(pattern, ''); alert(result+" "+result.length); pattern = /\s+$/; result = result.replace(pattern, ''); alert(result+" "+result.length); pattern = /\s+/g; result = result.replace(pattern, ''); alert(result+" "+result.length); 5、简单的电子邮件验证 var pattern = /^([a-zA-Z0-9_\.\-]+)@([a-zA-Z0-9_\.\-]+)\.([a-zA-Z]{2,4})$/; var str = 'yc60.com@gmail.com'; alert(pattern.test(str)); var pattern = /^([\w\.\-]+)@([\w\.\-]+)\.([\w]{2,4})$/; var str = 'yc60.com@gmail.com'; alert(pattern.test(str));

七、支持正则表达式的字符串方法

方法	描述
search	检索与正则表达式相匹配的第一个匹配项的索引。
match	找到一个或多个正则表达式的匹配。
replace	替换与正则表达式匹配的子串。
split	把字符串分割为字符串数组。

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