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This article is to share with you about the use of question marks in JavaScript regular expressions, the editor thinks it is very practical, so I share it with you to learn. I hope you can get something after reading this article.

Put a question mark after the character that indicates repetition, such as +?, *?, {2pr 3}? A greedy pattern that can stop matching.

Var pattern=/\ w {2pattern2 3} /; console.log ("aaaa" .match (match) [0]); / * result "aaa"; in greedy mode, there are as many matches as possible, so three repetitive characters * / var pattern2=/\ w {2Yue3}? /; console.log ("aaaa" .match (match) [0]); / * result "aa" After adding the question mark, it will match as few repetitions as possible, * so it matches to 2 repeated characters * /

Using?: within a group can produce unnumbered groups, such as

Var pattern=/ (ab)\ w + (ba) /; console.log ("abcba_" .replace (pattern, "$1")); / * result "ab_"; matching characters are replaced by the first grouping (ab) * / var pattern2=/ (?: ab)\ w + (ba) /; console.log ("abcba_" .replace (pattern2, "$1")); / * result "ba_" A?: is added to the first grouping, resulting in a * unnumbered grouping, so the character matching $1 is the second grouping, * that is, the text content matched by the first numbered grouping (ba) * /

(? =) and (?!); zero width positive assertions and negative assertions, with parentheses indicating that the right side of a position must match the right side of the =, or disagree! The characters after the match.

Var pattern=/str (? = ings) ing/;console.log ("strings.a" .match (pattern)); console.log ("strings.a" .match (? = 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 position after r must be the same as * ings; and / string (? = s) /; the match "string"; the position after g must be followed by an s to the right. " "string_x" also contains "string" but * is not satisfied (? =...) Conditions in parentheses * / var pattern=/string (?! s) /; console.log ("strings" .match (pattern)); / / nullconsole.log ("string." .match (pattern)); / / ["string"] / * (?!...) It can't be on the right side of a certain position! After matching characters, * string (?! s) / match "string", "g" cannot be followed by "s" * / above are the use of question marks in JavaScript regular expressions. The editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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