JavaScript - How To Count String Occurrence in String?

Last Updated : 27 Nov, 2024

Here are the various methods to count string occurrence in a string using JavaScript.

1. Using match() Method (Common Approach)

The match() method is a simple and effective way to count occurrences using a regular expression. It returns an array of all matches, and the length of the array gives the count.

JavaScript

const s1 = "hello world, hello JavaScript!"; const s2 = "hello"; const count = (s1.match(new RegExp(s2, "g")) || []).length; console.log(count);

Output

new RegExp(word, "g"): Creates a global regular expression for the target word.
match(): Returns an array of matches.
|| []: Handles cases where no matches are found (returns an empty array).

2. Using while Loop

You can manually iterate through the string to count occurrences by checking for the substring at each position.

JavaScript

const s1 = "hello world, hello JavaScript!"; const s2 = "hello"; let count = 0; let pos = 0;  while ((pos = s1.indexOf(s2, pos)) !== -1) {     count++;     // Move past the current match     pos += s2.length;  } console.log(count);

Output

indexOf(s2, pos): Finds the position of the substring starting from pos.
pos += s2.length: Advances the position to avoid counting overlapping matches.

3. Using split() Function

By splitting the string at each occurrence of the target substring, the resulting array.length-1 will give the count.

JavaScript

const s1 = "hello world, hello JavaScript!"; const s2 = "hello"; const count = s1.split(s2).length - 1; console.log(count);

Output

split(word): Splits the string at every occurrence of the substring.
length - 1: The number of occurrences equals the number of splits minus one.

4. Using indexOf() in a Loop

Another approach using indexOf() involves repeatedly searching for the substring.

JavaScript

const s1 = "hello world, hello JavaScript!"; const s2 = "hello"; let count = 0; let pos = s1.indexOf(s2);  while (pos !== -1) {     count++;     pos = s1.indexOf(s2, pos + s2.length); } console.log(count);

Output

indexOf(word, start): Finds the substring starting from the specified index.
The loop continues until indexOf() returns -1 (no more matches).

5. Using Regular Expressions

Regular expressions offer a concise and powerful way to count substring occurrences.

JavaScript

const s1 = "hello world, hello JavaScript!"; const s2 = "hello"; const regex = new RegExp(s2, "g"); const count = (s1.match(regex) || []).length; console.log(count);

Output

RegExp(word, "g"): Enables global matching of the substring.
match(): Returns all matches as an array.

6. Using reduce() Method

You can use reduce() to iterate through an array representation of the string (e.g., split by spaces) and count matches.

JavaScript

const s1 = "hello world, hello JavaScript!"; const s2 = "hello"; const count = s1.split(" ")     .reduce((acc, curr) =>          (curr === s2 ? acc + 1 : acc), 0); console.log(count);

Output

split(" "): Breaks the string into an array of words.
reduce(): Accumulates the count by comparing each element with the target word.

7. Using includes() and slice() Methods

You can use includes() to check for the substring and slice() to move past each match.

JavaScript

const s1 = "hello world, hello JavaScript!"; const s2 = "hello"; let count = 0; let temp = s1;  while (temp.includes(s2)) {     count++;     temp = temp.slice(temp.indexOf(s2) + s2.length); } console.log(count);

Output

includes(word): Checks if the substring exists in the string.
slice(): Creates a new substring starting after the current match.