I am exploring capturing groups in Regex and I am getting confused about lack of documentation on it. For ex, can anyone tell me difference between two regex:
/(?:madhur)?/
and
/(madhur)?/
As per me, ? in second suggests matching madhur
zero or once in the string.
How is the first different from second ?
The first one won't store the capturing group, eg $1
will be empty. The ?:
prefix makes it a non capturing group . This is usually done for better performance and un-cluttering of back references.
In the second example, the characters in the capturing group will be stored in the backreference $1
.
Here's the most obvious example:
"madhur".replace(/(madhur)?/, "$1 ahuja"); // returns "madhur ahuja"
"madhur".replace(/(?:madhur)?/, "$1 ahuja"); // returns "$1 ahuja"
Backreferences are stored in order such that the first match can be recalled with $1
, the second with $2
, etc. If you capture a match (ie (...)
instead of (?:...)
), you can use these, and if you don't then there's nothing special. As another example, consider the following:
/(mad)hur/.exec("madhur"); // returns an array ["madhur", "mad"]
/(?:mad)hur/.exec("madhur"); // returns an array ["madhur"]
It doesn't affect the matching at all.
It tells the regex engine
replace()
method exec()
method and
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.