How do I Replace all Occurrences of a String in JavaScript?

Matthew C.

—December 15, 2022

The Problem

You want to replace all occurrences of a substring in a string. This could be a character, a word, or multiple words. For example, you want to kebab case a string of words:

const myString = "the quick brown fox";

You need to replace all the empty spaces with a -. How do you do this?

The Solution

The simplest and best way to replace multiple occurrences of a substring in a string is to use the replaceAll method. There are other methods you can use if you need to support older browsers.

The replaceAll() Method

The replaceAll() method has two arguments: pattern and replacement. It returns a new string with all matches of the pattern replaced by a replacement. The pattern is a string or regular expression (RegExp). The replacement is a string or function called for each match.

To replace all the empty spaces with a - in the example string below, you can call replaceAll() with the following two string arguments:

const myString = "the quick brown fox";
const result = myString.replaceAll(" ", "-");
console.log(result); // the-quick-brown-fox

Using a regular expression for the pattern argument is useful for more complex replacements, such as case-insensitive replacements:

const myString = "Apples pears apples strawberries";
const pattern = /apples/gi;
const replacement = "grapes";

const result = myString.replaceAll(pattern, replacement);
console.log(result); // grapes pears grapes strawberries

If the pattern argument uses a regular expression, it must be a global regular expression. This is indicated by the g flag. If you don’t add the g flag, you’ll get the following error:

Uncaught TypeError: replaceAll must be called with a global RegExp

The replaceAll() method is relatively new. It was introduced in ES2021 and works with all major browsers. If you have to support older versions of browsers, check that they support replaceAll().

The replace() Method

The replace() method is similar to the replaceAll() method, the difference being that if the pattern argument is a string, only the first occurrence will be replaced. You can get the replace() method to replace all occurrences by using a global regular expression for the pattern argument:

const myString = "Apples pears apples strawberries";
const pattern = /apples/gi;
const replacement = "grapes";

const result = myString.replace(pattern, replacement);
console.log(result); // grapes pears grapes strawberries

Using split() and join()

You can also replace all occurrences of a string by first passing in the substring to be replaced in the split() method and then using the join() method to join the returned array with the new substring.

The split() method searches for the passed-in separator argument in the string. The separator is the pattern that describes where each split should occur — the substring to be replaced. The split() method returns an array of strings, split at each point where the separator occurs.

The join() method returns a new string by concatenating all of the elements in the array returned by the split() method. The array elements are joined using the new replacement substring.

const myString = "the quick brown fox";

const resultArr = myString.split(" ");
console.log(resultArr); // [ "the", "quick", "brown", "fox" ]
console.log(resultArr.join("-")); // the-quick-brown-fox

This method is not suitable for more complex replacements, such as case-insensitive replacements.