Javascript Regular Expression summary, Regular Expression

Javascript Regular Expression summary, Regular Expression

Tools

Regexpal is an online Javascript Regular Expression processor with address: http://www.regexpal.com

Learning regular expressions is important to practice. For example:

Matched number: 707-827-7019

Character group match

[0-9] [0-9] [0-9]-[0-9] [0-9] [0-9]-[0-9] [0-9- 9] [0-9] [0-9]
\ D match any Arabic numerals
\ D match any non-Arabic number

. Match any character

\ D \ D \ d
\ D.

Capture groups and backward applications

Use parentheses () to create a group and use \ 1 to reference the captured group content.

(\ D) \ d \ 1 matches 707

Complete matching number:

^ (\ D {3} \) | ^ \ d {3} [.-]?)? \ D {3} [.-]? \ D {4} $
^ Indicates the starting position of a row
(Indicates the start character of the capture group.
\ (Left parenthesis
\ D {3} indicates matching three digits
\) Represents the right parenthesis
| Indicates Selection
[.-]? Match an optional dot or hyphen
) Capture group Terminator
? Indicates that the group is optional.
$ Indicates that the row ends.

Boundary

Use the escape character to match the starting position of a line or string ^
Use the dollar sign to match the end of a row or string $

Quantifiers

The quantifiers are greedy by default.
Greedy quantifiers match the entire string first. When a match is attempted, the system selects as much content as possible, that is, the entire input. The quantifiers match the entire character first. If it fails, a character will be rolled back and tried again. This process is called backtracking.
Lazy quantifiers start from the starting position of the target to search for matching. Each time you check a character in a string, you can find the matching content. Finally, he will try to match the entire string.
A placeholder quantizer will overwrite the entire target and then try to find the matching content. However, it only tries once and does not backtrack.
If you use. * to match any character Zero or multiple times

Greedy quantifiers

You can use curly braces {} to limit the number of times a pattern matches within a certain range. In addition, the unmodified quantifiers are greedy quantifiers.
7 {1,} and 7 +
7 {0,} and 7 *
7? And 7 {0, 1}
Essentially the same
7 {m, n} matches m to n times

Lazy Quantizer

ADD? The quantifiers become lazy.
7 ?? First 7? Matches zero or one 7, and will not match any content after laziness
7 *? Match zero 7
7 +? Match A 7
7 {m, n }? Match m 7

For regular expression matching html and xml tags, write them again next time.

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