Regular Expression: Quantifiers

Summary: in this tutorial, you’ll learn to use quantifiers to match several instances of a character, group, or character class in a string.

Quantifiers specify how many instances of a character, group, or character class must appear in the input string for a match to be found.

Quantity

Exact count {n}

A number in curly braces {n}is the simplest quantifier. When you append it to a character or character class, it specifies how many characters or character classes you want to match.

For example, the regular expression /\d{4}/ matches a four-digit number. It is the same as /\d\d\d\d/:

let str = 'ECMAScript 2020';
let re = /\d{4}/;

let result = str.match(re);

console.log(result);Code language: JavaScript (javascript)

Output:

['2020', index: 11, input: 'ECMAScript 2020', groups: undefined]Code language: JavaScript (javascript)

The range {n,m}

The range matches a character or character class from n to m times.

For example, to find numbers that have two, three, or four digits, you use the regular expression /\d{2,4}/g:

let str = 'The official name of ES11 is ES2020';
let re = /\d{2,4}/g;

let result = str.match(re);
console.log(result);
Code language: JavaScript (javascript)

Output:

["11", "2020"]Code language: JavaScript (javascript)

Because the upper limit is optional, the {n,} searches for a sequence of n or more times. For example, the regular expression /\d{2,}/ will match any number that has two or more digits.

let str = 'The official name of ES6 is ES2015';
let re = /\d{2,}/g;

let result = str.match(re);
console.log(result);
Code language: JavaScript (javascript)

Output:

["2015"]Code language: JavaScript (javascript)

The following example uses the regular expression /\d{1,}/g to match any numbers that have one or more digits in a phone number:

let numbers = '+1-(408)-555-0105'.match(/\d{1,}/g);
console.log(numbers);Code language: JavaScript (javascript)

Output:

["1", "408", "555", "0105"]
Code language: JavaScript (javascript)

Shorthands

+

The quantifier {1,} means one or more which has the shorthand as +. For example, the \d+ searches for numbers:

let phone = "+1-(408)-555-0105";
let result = phone.match(/\d+/g);

console.log(result);
Code language: JavaScript (javascript)

Output:

["1", "408", "555", "0105"]Code language: JavaScript (javascript)

?

The quantifier ? means zero or one. It is the same as {0,1}. For example, /colou?r/ will match both color and colour:

let str = 'Is this color or colour?';
let result = str.match(/colou?r/g);

console.log(result);Code language: JavaScript (javascript)

Output:

["color", "colour"]Code language: JavaScript (javascript)

*

The quantifier * means zero or more. It is the same as {0,}. The following example shows how to use the quantifier * to match the string Java followed by any word character:

let str = 'JavaScript is not Java';
let re = /Java\w*/g

let results = str.match(re);
console.log(results);
Code language: JavaScript (javascript)

Output:

["JavaScript", "Java"]
Code language: JavaScript (javascript)

We often use quantifiers to form complex regular expressions. The following shows some regular expression examples that include quantifiers:

• Whole numbers:/^\d+$/
• Decimal numbers:/^\d*.\d+$/
• Whole numbers and decimal numbers:/^\d*(.\d+)?$/
• Negative, positive whole numbers & decimal numbers:/^-?\d*(.\d+)?$/

Summary

The following table lists the quantifiers: