Several usages of the question mark of JS regular expression

Add a question mark after the character that represents the repetition, such as +?,*?,{2,3}? You can stop a matching greedy pattern.

1 varpattern=/\w{2,3}/;2Console.log ("AAAA". Match (pattern) [0]);3 /*The result is "AAA"; the greedy mode will match as many as possible,4 so it matches 3 duplicate characters.5 */6 varpattern2=/\w{2,3}?/;7Console.log ("AAAA". Match (PATTERN2) [0]);8 /*9 * result "AA"; add question mark will be as few as possible to match the number of repetitions,Ten * So match to 2 duplicate characters One */

Use within a group?: You can generate non-numbered groupings, such as

1  varpattern=/(AB) \w+ (BA)/;2Console.log ("Abcba_". Replace (Pattern, "$"));3   /*The result "ab_"; the character matched to the first group (AB)4 * Replace5  */6   varpattern2=/(?: AB) \w+ (BA)/;7Console.log ("Abcba_". Replace (PATTERN2, "$"));8   /*9 * result "ba_"; added in the first group?:, produces aTen * There are no numbered groupings, so the matching characters are the second grouping, One * That is, the first number grouping (BA) matches the text content A  */

(? =) and (?!); 0 wide forward assertion and negative assertion, in parentheses indicates that the right side of a position must be matched to the right of =, or not to match the character after.

1 varPattern=/str (? =ings) ing/;2Console.log ("STRINGS.A". Match (pattern));3Console.log ("Strings.a". Match (/string (? =s)/));4Console.log ("String_x". Match (pattern));5Console.log ("String_x". Match (/string (? =s)/));6 /*The first two results are ["string"], and the latter two results are null;7 */STR (? =ings) ing/matches "string", and R to the right of the position must be followed by8* Upper Ings; and/string (? =s)/same as; Match "string"; The position behind the G9* The right side must be followed by an S. "String_x", although it also contains "string"butTen* Not satisfied (? =...) The conditions in parentheses One*/

1 var pattern=/string (?! s)/; 2 console.log ("strings". Match (pattern)); // NULL 3 console.log ("string.". Match (pattern)); // ["string"] 4 /* (?! ...) The right side of a position cannot have! After matching characters,5*/string (?! s)/Match "string", "G" cannot be followed by "s"6 */

Represents repeated 0 or 1 times when the number of repetitions is expressed

Several usages of the question mark of JS regular expression