Regular Expressions in JS <<<

About Regular Expressions:　

　　A regular expression is a logical formula for a string (including ordinary characters (for example, letters between A and z) and special characters (called "metacharacters"), which is a "rule string" that is composed of a predefined set of characters, and a combination of those specific characters, which Used to express a filtering logic for a string. A regular expression is a text pattern that describes one or more strings to match when searching for text.

Declaration of a regular expression

1, the literal declaration:

/Regular Expression rule/match pattern

Example:var reg =/^abc$/i;

2, the NEW keyword statement:

　　　var reg = new RegExp ("^abc$", I);

Ii. description of regular expression rules

　　Rule description:

Symbol	Describe
/.../	Represents the beginning and end of a pattern
^	Match the start of a string
$	Match the end of a string
\s	Any whitespace character
\s	Any non-whitespace character
\d	Matches a numeric character, equivalent to [0-9]
\d	Any character other than a number, equivalent to [^0-9]
\w	Match a number, underscore, or alphabetic character, equivalent to [a-za-z0-9]
\w	Any non-single character, equivalent to [^a-za-z0-9_]
.	Any character other than a line break

quantifier Description:

Symbol	Describe
N	Matches the previous n times
{N,}	Matches the previous item n times, or multiple times
{N,m}	Match the previous item at least n times, but not more than m times
*	Matches the previous item 0 or more times, equivalent to {0,}
+	Matches the previous item 1 or more times, equivalent to {1,}
?	Matches the previous item 0 or 1 times, which means the previous item is optional

　　Symbol:

Symbol	Describe
|	Match any one of the selected characters, such as P|q, to match Q or P
()	Group
[]	The data to match
^	Take counter

Common patterns of regular expressions

1,G means global match . No g indicates that only the first qualifying string is matched;

        "AAA". Replace (/a/, "*"); --"*AA"      

2,I means ignoring case matching , and the default case must also conform to the regular requirements.

    "AAa". Replace (/a/, "#"); --"a#a" "         AAA". Replace (/a/i, "#"), "#Aa"     "AAA". Replace (/a/gi, "#")--"# #"

3,m indicates multi-line matching mode:

If not with M, the string represents only one end of the beginning;

If you have M, you can have multiple endings at the beginning for multiple lines of string.

Example One:
varStr= "This is an\n antzone good"; varreg=/an$/;　　Console.log (Str.match (reg)); Could not match string"An", although "an"The following line has been wrapped, but not a multiline match, so it is not the end of the string line. Example two:varStr= "This is an\n antzone good"; varreg=/an$/m; Console.log (Str.match (reg));
Can match string"An"because a multi-line match is used. Example three:varReg =/^b/;varstr = ' Test\nbbs '; Execreg (REG,STR);
The match failed because there is no B character at the beginning of the string. But after adding the M modifier: example four:varReg =/^b/m; varstr = ' Test\nbbs '; Execreg (REG,STR);
Match to B, because after the M modifier is added,^ has already indicated the beginning of the line, because BBS at the beginning of the second row of the string, so it can be successfully matched.

[ Multi-line string]

① string with \ n for line break: "Abc\nabc". Replace (/^A/GM, "*");

②ES6 can be used to denote a string, a string that supports direct line wrapping.

4. Detection method

(1)reg.test (str): Detects whether a string conforms to the regular requirement and returns TRUE or false.

(2)reg.exec (str): Detects whether a string conforms to the regular requirement, conforms to the returned array, and does not conform to return NULL.

Returns the format of the array:

①index Property: Represents the string, the first few characters, and begins to match the regular.

②input Property: Represents the complete retrieved string.

③ Subscript No. 0: Represents a string substring that conforms to a regular requirement.

④ subscript from 1: Represents a string substring that matches the () package in the regular. In other words, there are several () in the regular, and there are several subscripts in the returned array.

Example:

/12 (3) (\d) 56/.exec ("aaa123056bbb");　

[ 　　　　 0: "123056", 1: "3", 2: "0", Index:3, input:< /c11> "AAA123056BBB", Length:3 ] 

Four, regular expressions commonly used validation exercises

1, verify the mailbox

var reg =/^[a-za-z0-9][email protected][a-za-z0-9]+\. [A-za-z]+ (\.[　　a-za-z]{2,3})? $/;　　 var mail = "[email protected]";  console.log (reg.test (mail));

2. Verify ZIP code (6-bit)

var reg =/^\d{5}$/;　　 var mailno = "251400"; Console.log (Reg.test (Mailno));

3, verify the mobile phone number (the first bit is 1, the second is 3/5/7/8, a total of 11)

var reg =/^1 (3|5|7|8) \d{9}$/;　　 var phone = "17862009622"; Console.log (Reg.test (phone));

4. Verification Age (1~120)

var reg =/^ (\d|[　　1-9]\d|1[01]\d|120) $/;  //  var reg =/^ ((1[0-1]|[ 1-9] \d|120) $/;　　var age = "121"; Console.log (Reg.test (age));　　

Regular Expressions in JS <<<