Quantifiers indicate numbers of characters or expressions to match.
Types
Note: In the following, item refers not only to singular characters, but also includes character classes, Unicode property escapes, groups and ranges.
Characters | Meaning |
---|---|
x* |
Matches the preceding item "x" 0 or more times. For example, |
x+ |
Matches the preceding item "x" 1 or more times. Equivalent to |
x? |
Matches the preceding item "x" 0 or 1 times. For example, If used immediately after any of the quantifiers |
x{n} |
Where "n" is a positive integer, matches exactly "n" occurrences of the preceding item "x". For example, |
x{n,} |
Where "n" is a positive integer, matches at least "n" occurrences of the preceding item "x". For example, |
x{n,m} |
Where "n" is 0 or a positive integer, "m" is a positive integer, and |
|
By default quantifiers like
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Examples
Repeated pattern
var wordEndingWithAs = /\w+a+\b/; var delicateMessage = "This is Spartaaaaaaa"; console.table(delicateMessage.match(wordEndingWithAs)); // [ "Spartaaaaaaa" ]
Counting characters
var singleLetterWord = /\b\w\b/g; var notSoLongWord = /\b\w{1,6}\b/g; var loooongWord = /\b\w{13,}\b/g; var sentence = "Why do I have to learn multiplication table?"; console.table(sentence.match(singleLetterWord)); // ["I"] console.table(sentence.match(notSoLongWord)); // [ "Why", "do", "I", "have", "to", "learn", "table" ] console.table(sentence.match(loooongWord)); // ["multiplication"]
Optional character
var britishText = "He asked his neighbour a favour."; var americanText = "He asked his neighbor a favor."; var 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"]
Greedy versus non-greedy
var text = "I must be getting somewhere near the centre of the earth."; var greedyRegexp = /[\w ]+/; // [\w ] a letter of the latin alphabet or a whitespace // + one or several times console.log(text.match(greedyRegexp)[0]); // "I must be getting somewhere near the centre of the earth" // almost all of the text matches (leaves out the dot character) var nonGreedyRegexp = /[\w ]+?/; // Notice the question mark console.log(text.match(nonGreedyRegexp)); // "I" // The match is the smallest one possible
Specifications
Specification |
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ECMAScript (ECMA-262) The definition of 'RegExp: Quantifiers' in that specification. |
Browser compatibility
For browser compatibility information, check out the main Regular Expressions compatibility table.