[Unsystematic memo] Full contact with JS Regular Expressions

Source: Internet
Author: User
    • The regular expression can be:
    • Modifier
The regular expression can be:

• Test a mode of a string. For example, you can test an input string to see if there is a phone number or a credit card number. This is called Data Validity verification.

• Replace text. You can use a regular expression in a document to identify a specific text, and then delete it all or replace it with another text.

• Extract a substring from the string based on the pattern match. It can be used to search for specific text in text or input fields.

Modifier Description
I Perform case-insensitive matching.
G Perform global match (search for all matches instead of stopping the first match ).
M Perform multi-row matching.

Other memos see http://www.w3school.com.cn/js/jsref_obj_regexp.asp



We will focus on analyzing some methods of JS Regular Expressions and their usage

Reg. Test (STR)
STR ="Certainly! He loves her! ";
Alert (Re. Test (STR ));//True, As long as it contains HE (HE), it will match. To only contain he or he, there cannot be other characters, you can use ^ and $

Exec and match
/* Regexpobject.exe C (string)
Returns an array containing matching results. If no match is found, the return value is null.
.VaRSometext ="Web2.0. net2.0";
VaRPattern =/(\ W +) (\ D) \. (\ D )/;
VaROutcome_exec = pattern.exe C (sometext );

The outcome_exec value is [Web2.0, web, 2, 0]. this is an array. if the expression 'pattern' is followed by a global G. the result is [Web2.0, web, 2, 0]. visible Exec

1. Always match

2. The returned array is the first matching result and a collection of group matching results.

If the regular expression does not have a global variable, String. Match returns the same result as exec. If G exists, match does not return the results captured by the group. For example

VaRSometext ="Web2.0. net2.0";
VaRPattern =/(\ W +) (\ D) \. (\ D )/;
VaROutcome_matc = sometext. Match (pattern );// Return values similar to arrays [, web,]
VaRPattern2 =/(\ W +) (\ D) \. (\ D)/g;
VaROutcome_matc2 = sometext. Match (pattern2); // return values similar to arrays [Web2.0, net2.0]

1. If no global variable exists, match is the same as exec.

2. If there is a global variable, match only returns the result set of the regular expression matching, and does not contain the results captured by any group.

PS: \ W is used. \ W is equivalent to [0-9a-za-z]. However, in the above expression (\ W +), it only matches the web, but does not match web2.

This is because if \ W is followed by \ D, \ W is only equivalent to [A-Za-Z]

Search, split, replace

Search returns the start index of the matching expression. The global variable is invalid.-1 is not found.

STR ="My age is 18. Golden Age! ";// The age is not certain. We cannot find its location using indexof.
Re =/\ D + /;
Alert (Str. Search (re ));// Return the searched string start subscript 10
// The followingCodeAlthough there is no error, the G mark is redundant.
Re =/\ D +/g;
Alert (Str. Search (re); // still 10


STR ="Some some \ tsome \ t \ f";
Re =/\ s + /;
Alert (Str. Replace (Re,"#"));// But this will only Replace the first pile of blank characters
// Because a regular expression can only be matched once, \ s + will exit after matching the first space.
Re =/\ s +/g;// G, global flag, will make the regular expression match the entire string
Alert (Str. Replace (Re,"@"));// Some @
// The other is similar to the split
VaRSTR ="A-BD-c";
VaRArr = Str. Split ("-");// Return ["A", "BD", "C"]
// If STR is input by the user, it may input a-BD-C or a bd c or a_bd_c, but not ABDC (in this case, it is wrong)
STR =A_db-c";// The user adds the separator s as he prefers.
Re =/[^ A-Z]/I;// As we mentioned earlier, ^ indicates the start of a character, but in [] it indicates a negative character set
// Match any character that is not within the specified range. All characters except letters are matched here.
Arr = Str. Split (re); // still return ["","BD","C"];
Complex replace applications
// Calculate the number of times a string has exceeded 9
VaR STR ="Adf9df9df9",// The string in the text file;
Re =/9/GI,// Match 9
Counter = 0;// Counter
Str. Replace (Re, function (){
Counter ++;// Every time a match occurs, the function is executed. The return value of the function is used to replace the original value.
Return "#";
// Finally, STR is changed to ADF # DF #"
FunctionF2c (s ){
VaRTest =/(\ D + (\. \ D *)?) F \ B/g;// Initialization mode.
Return(S. Replace (test,Function($0, $1, $2 ){
Return($1-32) * 5/9) +"C");
Document. Write (f2c ("Water freezes at 32f and boils at 212f ."));
// Water freezes at 0C and boils at 100C.
PS: when the second parameter in the replace method is a function, $0, $1... is included in the function ..... $ N represents the subcapture of a regular expression.
Replace does not update the global attribute of Regexp.

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