Count the Number of Digits in a String in JavaScript

Count the Number of Digits in a String #

To count the number of digits in a string, use the replace() method to replace all non digit characters with an empty string and access the length property on the result. The replace method returns a new string with the matches replaced.

index.js

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function getCountOfDigits(str) {
  return str.replace(/[^0-9]/g, '').length;
}

console.log(getCountOfDigits('12hello34')); // 👉️ 4
console.log(getCountOfDigits('hello')); // 👉️ 0
console.log(getCountOfDigits('hello12.5')); // 👉️ 3

We used the String.replace method to replace all non-digit characters in the string, so we can get the length of the string containing only digits.

The first parameter we passed to the replace method is a regular expression and the second a replacement for each match of the result expression in the string.

The forward slashes / / mark the beginning and end of the regular expression.

The part between the square brackets [] is called a character class.

The caret ^ symbol means "not the following", in other words we're matching anything but a range of digits from 0-9.

We used the g (global) flag, because we want to match all occurrences of non-digit characters in the string and not just the first occurrence.

If you ever need help reading a regular expression, check out this regex cheatsheet from MDN. It's by far the best one out there.

The second parameter we passed to the replace method is a replacement string for each match. Because we want to remove all non-digit characters, we provided an empty string.

The replace method does not change the contents of the original string, it returns a new string. Strings are immutable in JavaScript.

In its entirety, the regular expression replaces all non-digit characters with an empty string.

index.js

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console.log('hello123'.replace(/[^0-9]/g, '')); // 👉️ 123

The last step is to access the length property on the new string, which gets us the number of digits in the original string.

Count the Number of Digits in a String in JavaScript