Matches the preceding item "x" 0 or more times. For example,
/bo*/ matches "boooo" in "A ghost booooed" and "b" in "A
bird warbled", but nothing in "A goat grunted".
x+
Matches the preceding item "x" 1 or more times. Equivalent to
{1,}. For example, /a+/ matches the "a" in
"candy" and all the "a"'s in "caaaaaaandy".
x?
Matches the preceding item "x" 0 or 1 times. For example,
/e?le?/ matches the "el" in "angel" and the "le" in
"angle."
If used immediately after any of the quantifiers *,
+, ?, or {}, makes the
quantifier non-greedy (matching the minimum number of times), as
opposed to the default, which is greedy (matching the maximum number
of times).
x{n}
Where "n" is a non-negative integer, matches exactly "n" occurrences of
the preceding item "x". For example, /a{2}/ doesn't match
the "a" in "candy", but it matches all of the "a"'s in "caandy", and
the first two "a"'s in "caaandy".
x{n,}
Where "n" is a non-negative integer, matches at least "n" occurrences of
the preceding item "x". For example, /a{2,}/ doesn't
match the "a" in "candy", but matches all of the a's in "caandy" and
in "caaaaaaandy".
x{n,m}
Where "n" and "m" are non-negative integers and m >= n,
matches at least "n" and at most "m" occurrences of the preceding
item "x". For example, /a{1,3}/ matches nothing in
"cndy", the "a" in "candy", the two "a"'s in "caandy", and the first
three "a"'s in "caaaaaaandy". Notice that when matching "caaaaaaandy",
the match is "aaa", even though the original string had more "a"s in
it.
x*? x+? x?? x{n}? x{n,}? x{n,m}?
By default quantifiers like * and + are
"greedy", meaning that they try to match as many times as
possible. The ? character after the quantifier makes the
quantifier "non-greedy": meaning that it will stop as soon as it finds the minimum number of matches. For example, given a string like "some <foo> <bar>
new </bar> </foo> thing":
/<.*>/ will match "<foo> <bar> new
</bar> </foo>"
/<.*?>/ will match "<foo>"
Note: Adding ? after {n} is syntactically valid but practically useless.
Since {n} always matches exactly n times, x{n}? behaves the same as x{n}.
In this example, we match words that either end with "our" or "or".
js
const britishText = "He asked his neighbour a favour.";
const americanText = "He asked his neighbor a favor.";
const regexpEnding = /\w+ou?r/g;
// \w+ One or several letters
// o followed by an "o",
// u? optionally followed by a "u"
// r followed by an "r"
console.table(britishText.match(regexpEnding));
// ["neighbour", "favour"]
console.table(americanText.match(regexpEnding));
// ["neighbor", "favor"]
In this example, we match one or more word characters or spaces with [\w ]+ and [\w ]+?. The first one is greedy and the second one is non-greedy. Note how the second one stops as soon as it meets the minimal requirement.
js
const text = "I must be getting somewhere near the center of the earth.";
const greedyRegexp = /[\w ]+/;
console.log(text.match(greedyRegexp)[0]);
// "I must be getting somewhere near the center of the earth"
// almost all of the text matches (leaves out the dot character)
const nonGreedyRegexp = /[\w ]+?/; // Notice the question mark
console.log(text.match(nonGreedyRegexp));
// "I"
// The match is the smallest one possible
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