How to Extract a Number from a String in JavaScript

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1. String replace() Method

To extract a number from a string in JavaScript, call the replace() method on the string with a regex to replace all the non-digit characters in the original string. For example:

const str = 'The number 345 has three digits';

const replaced = str.replace(/\D/g, '');
console.log(replaced); // 345

The String replace() method returns a new string with the matches of a pattern replaced by a replacement. We pass a regular expression that matches all the non-digit characters so that we can replace them with an empty string ('') to remove them.

The \D regex metacharacter matches any non-digit characters in a string.

The g (global) flag specifies that every occurrence of a non-digit character in the string should be matched by the regex.

If we don’t pass the global flag, only the first non-digit character in the input string will be matched and replaced:

const str = 'The number 345 has three digits';

// No 'g' flag in regex
const replaced = str.replace(/\D/, '');

console.log(replaced); // he number 345 has three digits

2. String match() Method

To extract a number from a string, we can also call the match() method on the string, passing a regex that matches a consecutive sequence of digits. For example:

const str = 'The number 345 has three digits';

const matches = str.match(/\d+/);
const numStr = matches[0];

console.log(numStr); // 345

The String match() method matches a string against a regular expression and returns the results. In our case, the matched number is the first item of the array, so we access the 0 property with bracket notation to get it.

The \d metacharacter is used to find a digit in a string. We add the + to \d in order to find a consecutive sequence of digits.

This second method is better when trying to extract each number in the string separately, as it treats a consecutive sequence of digits as a separate match. To extract each number separately, we’ll need to add the g flag:

const str = 'The numbers 345 and 847 have three digits';

const matches = str.match(/\d+/g);
console.log(matches); // [ '345', '847' ]

const str = 'There are no numbers in this string';

const matches = str.match(/\d+/g);
console.log(matches); // null

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