Several usage summaries of question marks in js regular expressions, and js Regular Expressions

Several usage summaries of question marks in js regular expressions, and js Regular Expressions

Add a question mark after a character that represents a repetition, for example, + ?, *?, {2, 3 }? You can stop matching greedy modes.

Var pattern =/\ w {2, 3}/; console. log ("aaaa ". match (pattern) [0]);/* result "aaa"; as many matches as possible in greedy mode, so it will match 3 repeated characters */var pattern2 =/\ w {2, 3 }? /; Console. log ("aaaa ". match (pattern2) [0]);/** result "aa"; after a question mark is added, the number of matching repetitions is as small as possible. * therefore, two duplicate characters are matched */

Used in a group? : Can generate unnumbered groups, such

Var pattern =/(AB) \ w + (ba)/; console. log ("abcba _". replace (pattern, "$1");/* result "AB _"; the matched characters are replaced by the first group (AB) */var pattern2 = /(? : AB) \ w + (ba)/; console. log ("abcba _". replace (pattern2, "$1");/** result "ba _"; added to the first group? :, Generates a * unnumbered group. Therefore, $1 matches the second group, and * is the text content matched by the first number group (ba */

(? =) And (?!); Zero-width positive-direction assertions and negative assertions. brackets indicate that the right side of a position must match the right side of =, or it cannot match! .

Var pattern =/str (? = Ings) ing/; console. log ("strings. a". match (pattern); console. log ("strings. a". match (/string (? = S)/); console. log ("string_x". match (pattern); console. log ("string_x". match (/string (? = S)/);/* The first two results are ["string"], and the last two results are null; * str (? = Ings) ing/matches "string". The right side of the r must be followed by * upper ings; And/string (? = S)/same; match "string"; the position behind g * must be on the right side of s. Although "string_x" also contains "string", * Does not meet (? =...) Conditions in parentheses */

Var pattern =/string (?! S)/; console. log ("strings ". match (pattern); // nullconsole. log ("string. ". match (pattern); // ["string"]/* (?!...) There cannot be one on the right of a location! * String (?! S)/matching "string", "g" cannot be followed by "s "*/

When it indicates the number of repeated times, it indicates that the number of repeated times is 0 or 1

Match the question mark of a regular expression

(? : Pattern) matches pattern but does not get the matching result. That is to say, this is a non-get match and is not stored for future use. This is useful when you use the "or" character (|) to combine each part of a pattern. For example, 'industr (? : Y | ies) is a simpler expression than 'industry | industries.
(?! Pattern) negative pre-query: matches the search string at the beginning of any string that does not match pattern. This is a non-get match, that is, the match does not need to be obtained for future use. For example, 'windows (?! 95 | 98 | NT | 2000) 'can match "Windows" in "Windows 3.1", but cannot match "Windows" in "Windows 2000 ". Pre-query does not consume characters. That is to say, after a match occurs, the next matching search starts immediately after the last match, instead of starting after the pre-query characters.
Reference: www.yesky.com/185/1932685.shtml

How do regular expressions match question marks?

\? Here, \ is a quote, for example ..