1, Regular expression: Verification (validation) of string -- string
Regular creation
Literal create / match string/
Instantiate object new RegExp('matching string ')
/ / double slash --- judge whether there are characters in the string that can match good
const reg1 = /good/
/ / short for regular expression
/ / instantiate the object
const reg2 = new RegExp('good')
console.log(reg1,reg2);
// /good/ /good/
2, Regular modifier
i ignore ignore case
var reg1 = /tmd/i
g global global
const reg2 = /tmd/g
/ / the first parameter of the constructor represents the matching character, and the second parameter represents the modifier
const reg3 = new RegExp('tmd','gi')
const str = 'hello tmd hei Tmd tmd'
/ / replace only replaces the first one by default
console.log(str.replace('tmd','**'));
console.log(str.replace(/tmd/ig,'**'));
console.log(str.replace(reg3,'**'));
3, Regular method
text() returns a Boolean value
exec() returns an array - always matches one. If it doesn't match, it returns null
Supplementary knowledge points
[ ] -> true
const reg = /tmd/ig
const str = 'hello tmd Tmd'
// The test regular method tests whether there is content matching the regular in the string -- Boolean values are generally sub regular, and global matching is not required
console.log(reg.test(str)); // true /
// It returns an array - always matches one. If it does not match, it returns null
console.log(reg.exec(str));
// ['Tmd', index: 10, input: 'hello tmd Tmd', groups: undefined]
4, Regular content
Regular syntax
| or
[] or (interval) [0-9] [1-9] [a-z] [A-Z] [0-9a-zA-Z]
Spaces will also be matched - generally regular do not write spaces
Regular metacharacter
Times matching
* 0 or more times {0,}
？ 0 or 1 times {0,1}
+ 1 or more {1,}
{m,n} m times to N times
{m,} at least m times
{m} m times
^ to start
$in ending
^ $can be used at the same time
. Match any character
5, Escape character
Escape use\
// Match\/
const reg = /\ \//
console.log(reg.test(' \/'));
// Match
const reg2 = /\./
// Match[
const reg3 = /\[/
console.log(reg3.test('[]]')); // true
console.log(reg2.test('hq')); // false
// + ? * {} the number of matches. You need something matching in front
// const reg4 = /+/
// Error reporting / + /: Nothing to repeat
const reg4 = /\+/
console.log(reg4.test('+')); // true
6, Abbreviation
\ d number
\ D non numeric
\ w # number, letter, underline [0-9a-zA-Z_]
\ W ， non numeric, alphabetic, underline
\ s # match white space characters
\ S # match non white space characters
White space characters are different from empty characters
Empty character {0}
7, Chinese
Chinese matching
[\u4e00-\u9fa5]
const reg = /^[\u4e00-\u9fa5]{3,6}$/
console.log(reg.test('How do you do')); // true
VIII. The method of using regular strings
charAt() accesses the value corresponding to the corner mark
charCodeAt() accesses the ASCII value of the value corresponding to the corner mark
String.fromCharCode() converts ASCII values to corresponding characters
includes() determines whether a value exists in the array
indexOf() determines whether a value exists in the array and returns the subscript that appears for the first time. If it cannot be found, it will be returned
Return - 1
lastIndexOf() determines whether a value exists in the array and returns the last subscript
slice(i,i) intercepts some values in the array and returns a new array
substring(i,i) / / intercept the 2nd to 3rd corner markers of (1,2)
substr(i, quantity) / / (2,2) cut 2 from the second
toUpperCase() upper case and toLowerCase() lower case
concat() + concatenate an array and return a new array
split() cuts the string into an array
replace(old,new) (only the first one will be replaced by default)
trim() removes the leading and trailing spaces
Regular methods are acceptable
Replace (to find, replace) will be replaced only once by default, so regular is required
search() is generally the same as indexOf, but search can also accept regular
match() finds the characters that meet the conditions. By default, only the first one will be found. Only global matching can find all the characters. If it cannot be found, null will be returned
split() cuts strings into arrays, which can also accept regular writing
// Replace sensitive words
function replaceMinGan(str,arr,n){
n = n || '**';
// const mgc = ['tmd','md','wc'];
const word = arr.join('|');
const reg = new RegExp(word,'ig')
return str.replace(reg,n)
}
const mgc = ['tmd','md','wc']
const res = replaceMinGan('wc,Regular truth tmd Easy,Wc',mgc)
console.log(res); // **, regular is so * * simple**
const str2 = 'good day day up'
console.log(str2.search('day'));
// 5 search = indexOf
console.log(str2.search(/da*y/gi));
// 5 regular search can be used, but indexOf cannot
console.log(str2.match(/da*y/gi)); // Characters ['day ','day'] that meet the criteria were found
const str3 = 'good good study day day up'
// Greedy matching
console.log(str3.split(/ +/));
// ['good', 'good', 'study', 'day', 'day', 'up']
9, Common regular exercises
/ / mailbox 123@qq.com 123@qq.cn 123@qq.com.cn
/ / there must be @, @ must be preceded by content Com or cn or com.cn end
const reg = /^[\w,\+]+@\w+\.(com|cn|com\.cn)$/
console.log(reg.test('1,+23@q.com.cn'));
// true
/ / ID number 18 digit 17 digit + digit or X
/ / ID card: 6 digits; 4 digits; year of birth: February 2; Date: 3 digits, or X
// ID number 18 digit 17 digit + digit or X
const reg2 = /^\d{17}[\dX]$/
console.log(reg2.test('22222219990929191X'));
// true
// The ID card has 6 digits, 4 digits, year of birth, February 2, date, 3 digits, or X
const reg3=/^\d{6}(19|20)\d{2}(0|1)\d(0|1|2|3)\d{4}[\dX]$/
console.log(reg3.test('22222219991929191X'));
// true
/ / delete all spaces
// Delete all spaces
const str = ' good good study day day up '
// const arr = ['',' ',' '] ...
// replace
console.log(str.replace(/ +/g,''));
// Replacing good study dayup with empty is equivalent to deleting it
/ / delete the leading and trailing spaces
console.log(str);
console.log(str.replace(/^ +| +$/g,''));
// good good study day day up
/ / delete extra spaces
console.log(str.replace(/ +/g,' '));
// good good study day day up