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This article mainly introduces which functions are commonly used in js regular expressions, which are very detailed and have certain reference value. Friends who are interested must finish reading them.

The method of regular expression object

1. Test, which returns a Boolean value indicating whether a pattern exists in the string being looked up. Returns true if it exists, false otherwise.

2. Exec, runs a lookup in a string with a regular expression pattern and returns an array containing the results of the lookup.

3. Compile, compiling regular expressions to an internal format for faster execution.

Properties of a regular expression object

1. Source, which returns a copy of the text of the regular expression pattern. Read only.

2. LastIndex, which returns the character position, which is the start position of the next successful match in the searched string.

3. Input ($_), which returns the string that performs the specification expression lookup. Read only.

4. LastMatch ($&), which returns the last matched character in any regular expression search. Read only.

5. LastParen ($+), if any, returns the last parenthesized submatch of any regular expression lookup. Read only.

6. LeftContext ($`), which returns the characters in the searched string from the beginning of the string to the position before the last match. Read only.

7. RightContext ($'), which returns the character from the last matching position to the end of the string being searched. Read only.

Some methods related to regular expressions for String objects

1. Match, find the match of one or more regular expressions.

2. Replace, replacing the substring that matches the regular expression.

3. Search, which retrieves the value that matches the regular expression.

4. Split, dividing the string into an array of strings.

Case 1 test method test

/ / test method, which tests the string and returns true if it matches the pattern, otherwise returns false var re = / he/;// the simplest regular expression, which matches the word he var str = "he"; console.log (re.test (str)); / / true str = "we"; console.log (re.test (str)); / / false str = "HE"; console.log (re.test (str)) / / false, uppercase, if you want to match both uppercase and lowercase, you can specify the I flag (I is the representation of ignoreCase or case-insensitive) re = / he/i; console.log (re.test (str)); / / true str = "certificates he loves her!"; console.log (re.test (str)); / / true, as long as it contains he (HE). If it is only he or HE and there are no other characters, you can use ^ and $re = / ^ he/i. / / delimited (^) represents the character start position console.log (re.test (str)); / / false, because he is not at the beginning of str str = "He is a good boy!"; console.log (re.test (str)); / / true,He is the character start position, and you also need to use $re = / ^ he$/i;//$ to indicate the character end position console.log (re.test (str)); / / false str = "He" Console.log (re.test (str)); / / true / / of course, you can't find out how powerful regular expressions are, because we can use = = or indexOf re = /\ s in the above example to match any white space characters, including spaces, tabs, page feeds, etc. Str= "user Name"; / / user name contains spaces console.log (re.test (str)); / / true str= "user Name" / / the user name contains the tabs console.log (re.test (str)); / / true re=/ ^ [Amurz] / ibank / [] matches any character within the specified range, where it matches the English alphabet and is not case-sensitive to str= "variableName"; / / the variable name must begin with the letter console.log (re.test (str)); / / true str= "123abc"; console.log (re.test (str)); / / false

Case 2 exec Test

Var haoVersion = "Haorooms 8"; / / where the 8 represents the system major version number var re = / ^ [a murz] +\ s +\ d represents a numeric console.log (re.test (haoVersion)). / / true, but we want to know the major version number / / another method exec, which returns an array, and the first element of the array is the complete matching content re=/ ^ [a murz] +\ s +\ d matching haoVersion I; arr = re.exec (haoVersion); console.log (arr [0]); / / outputs the haoVersion in full, because the whole string matches re / / I only need to fetch the number re=/\ dstring; var arr = re.exec (haoVersion) The first to n elements of the array returned by console.log (arr [0]); / / 8 / / exec contain any submatch re=/ ^ [amurz] +\ s + (\ d +) $/ ibank / use () to create a submatch arr = re.exec (haoVersion); console.log (arr [0]); / / the entire haoVersion, that is, the complete matching console.log of the regular expression (arr [1]) / / 8, the first child matches, in fact, you can also take out the major version number console.log (arr.length); / / 2 haoVersion = "Haorooms 8.10"; / / take out the major version number and the minor version number re = / ^ [a murz] +\ s + (\ d +)\. (\ d +) $/ I hand. Is one of the metacharacters of regular expressions. To use its literal meaning, you must escape arr = re.exec (haoVersion); console.log (arr [0]); / / full haoVersion console.log (arr [1]); / / 8 console.log (arr [2]); / / 10

Case 3 some methods related to regular expressions for String objects

1. About replace, my previous blog was devoted to it. You can also pass parameters.

2. Other operations

/ / replace method to replace the string var str = "some money"; console.log (str.replace ("some", "much")); / / much money / / replace the first parameter can be the regular expression var re = /\ s var re / white space character console.log (str.replace (re, "%")) / / some%money / / regular expressions are extremely convenient when you don't know how many white space characters are in a string: str = "some some\ tsome\ t\ f"; re = /\ sblank; console.log (str.replace (re, "#")) / / but this will only replace the pile of white space characters that appear for the first time / / because a regular expression can only be matched once.\ s + after matching the first space, it exits re = /\ s white space, the global flag, which makes the regular expression match the entire string console.log (str.replace (re, "@"). / / some@some@some@ / / another similar is split var str = "a-bd-c"; var arr = str.split ("-"); / / return ["a", "bd", "c"] / / if the str is entered by the user, he may enter a-bd-c or abdc or a_bd_c, but it will not be abdc (so he mistyped) str = "a_db-c" / / the user adds the delimiter s re=/ [^ a murz] / iTabash / before we say ^ indicates the beginning of the character, but in [] it represents a negative character set / / matches any character that is not within the specified range, here it matches all characters except letters arr = str.split (re); / / still returns ["a", "bd", "c"] / / We often use indexOf when looking in a string, and the method applied to regular search is search str = "My age is 18.Golden age!"; / / the age is not fixed, we can't find its location with indexOf re = /\ dcalendar console.log; console.log (str.search (re)) / / return the found string to start the subscript 10 / / Note, because the search itself is returned as soon as it appears for the first time, there is no need to use the g flag / / in search. Although the following code does not make an error, the g flag is superfluous re=/\ dimpulse g; console.log (str.search (re)); / / it is still 10 var str = "My name is CJ.Hello everyone!"; var re=/ [aforesz] / / / matches all uppercase letters var arr = str.match (re); / / returns the array console.log (arr); / / the array will contain only one M because we do not use the global match re = / [Amurz] / g; arr = str.match (re); console.log (arr); / / the word re = /\ b [a-z] *\ b/gi is extracted from the string / /\ b indicates the word boundary str = "one two three four"; console.log (str.match (re)); / / one,two,three,four

Case 4 some properties of the RegExp object instance

Var re = / [Amurz] / I; console.log (re.source); / / output the [Amurz] string / / Please note that the direct console.log (re) outputs the regular expression along with the forward slash and flag, which is var re = / [Amurz] / defined by the re.toString method; / / after the exec method is executed, the lastIndex property of the re is modified, var str = "HelloLighting Worldling!"; var arr = re.exec (str) Console.log (re.lastIndex); / / 0, because the global flag re = / [Amurz] / g; arr = re.exec (str); console.log (re.lastIndex); / / 1 arr = re.exec (str); console.log (re.lastIndex); / / 7 var re = / [Amurz] /; var str = "HelloLines Worldhands!"; re.lastIndex = 120; var arr = re.exec (str); console.log (re.lastIndex); / / 0

Case 5 static properties of the RegExp object

/ / the last string used to match (the string passed to the test,exec method) var re = / [Amurz] /; var str = "var arr re.exec (str); console.log (RegExp.input); / / Hellother Worldhands! Re.exec ("tempstr"); console.log (RegExp.input); / / is still HelloGrad Worldwide matching characters, because tempstr does not match / / lastMatch's last matching character re = / [a murz] / g; str = "hi"; re.test (str); console.log (RegExp.lastMatch); / / h re.test (str); console.log (RegExp ["$&"]) / / I, $& is the short name of lastMatch, but since it is not a legal variable name, you should. / / the last matching packet of lastParen re = / [a Murz] (\ d +) / gi; str = "Class1 Class2 Class3"; re.test (str); console.log (RegExp.lastParen); / / 1 re.test (str); console.log (RegExp ["$+"]) / / 2 / / leftContext returns the characters in the searched string from the beginning of the string to the position before the last match / / rigthContext returns the characters in the searched string between the beginning of the last matching position and the end of the string re = / [Amurz] / g; str = "123ABC456"; re.test (str); console.log (RegExp.leftContext); / / 123 console.log (RegExp.rightContext); / / BC456 re.test (str) Console.log (RegExp ["$`]); / / 123A console.log (RegExp [" $'"]); / / C456

Case 6 uses the RegExp constructor to note

Var str = "\?"; console.log (str); / / only output? Var re = /\? / / will match? Console.log (re.test (str)); / / true re = new RegExp ("\?"); / / error because\ is an escaped character in the string\? Equivalent to? To get it, you need it. Re = new RegExp ("\\?"); / / correct, will match? Console.log (re.test (str)); / / true uses the special character / / ASCII in regular expressions to represent the special character var re = / ^\ x43\ x4A in hexadecimal numbers / will match CJ console.log (re.test ("CJ")); / / true / / can also be used in octal mode re = / ^\ 103\ 112 $/; / / will match CJ console.log (re.test ("CJ")) / / true / / you can also use Unicode to encode re = / ^\ u0043\ u004A encoding / use Unicode, which must start with u, followed by the four-digit hexadecimal representation of character encoding console.log ("CJ"). These are all the contents of this article entitled "what are the common functions of js regular expressions?" Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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