Groups and ranges
Groups and ranges indicate groups and ranges of expression characters.
Types
Characters | Meaning |
---|---|
x|y |
Matches either "x" or "y". For example,
|
[xyz] |
A character class. Matches any one of the enclosed characters. You can specify a range of characters by using a hyphen, but if the hyphen appears as the first or last character enclosed in the square brackets it is taken as a literal hyphen to be included in the character class as a normal character.
For example,
For example,
For example, |
|
A negated or complemented character class. That is, it matches
anything that is not enclosed in the brackets. You can specify a range
of characters by using a hyphen, but if the hyphen appears as the
first or last character enclosed in the square brackets it is taken as
a literal hyphen to be included in the character class as a normal
character. For example, Note: The ^ character may also indicate the beginning of input. |
(x) |
Capturing group: Matches
A regular expression may have multiple capturing groups. In results,
matches to capturing groups typically in an array whose members are in
the same order as the left parentheses in the capturing group. This is
usually just the order of the capturing groups themselves. This
becomes important when capturing groups are nested. Matches are
accessed using the index of the result's elements ( Capturing groups have a performance penalty. If you don't need the matched substring to be recalled, prefer non-capturing parentheses (see below).
|
\n |
Where "n" is a positive integer. A back reference to the last
substring matching the n parenthetical in the regular expression
(counting left parentheses). For example,
|
\k<Name> |
A back reference to the last substring matching the
Named capture group specified by
For example,
Note: |
(?<Name>x) |
Named capturing group: Matches "x" and stores it on
the groups property of the returned matches under the name specified
by
For example, to extract the United States area code from a phone
number, we could use |
(?:x) |
Non-capturing group: Matches "x" but does not remember
the match. The matched substring cannot be recalled from the resulting
array's elements ([1], ..., [n] ) or from the predefined
RegExp object's properties ($1, ..., $9 ).
|
Examples
Counting vowels
var aliceExcerpt = "There was a long silence after this, and Alice could only hear whispers now and then.";
var regexpVowels = /[AEIOUYaeiouy]/g;
console.log("Number of vowels:", aliceExcerpt.match(regexpVowels).length);
// Number of vowels: 26
Using groups
let personList = `First_Name: John, Last_Name: Doe
First_Name: Jane, Last_Name: Smith`;
let regexpNames = /First_Name: (\w+), Last_Name: (\w+)/mg;
let match = regexpNames.exec(personList);
do {
console.log(`Hello ${match[1]} ${match[2]}`);
} while((match = regexpNames.exec(personList)) !== null);
Using named groups
let personList = `First_Name: John, Last_Name: Doe
First_Name: Jane, Last_Name: Smith`;
let regexpNames = /First_Name: (?<firstname>\w+), Last_Name: (?<lastname>\w+)/mg;
let match = regexpNames.exec(personList);
do {
console.log(`Hello ${match.groups.firstname} ${match.groups.lastname}`);
} while((match = regexpNames.exec(personList)) !== null);