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Formatting Numbers with Commas in JavaScript: Two Methods Compared

Imagine writing an article without including commas. It would be hard to understand, right?

Commas are an essential part of our written language; they separate things, and they are used to help us understand written communication better. Now imagine writing a large number without commas – it’s not easy to read, is it?

Formatting numbers with commas helps with comprehension and makes them easier to read. In this article, we will discuss two methods of formatting numbers with commas in JavaScript: toLocaleString() and regular expressions with String.replace().

Formatting Numbers with Commas Using toLocaleString() Method

The toLocaleString() method is a built-in JavaScript function that returns a string with a variable number format. The number is split up into groups of three, and a comma is placed between each group.

This is known as a “comma-separated string,” which is easier to read and understand than an unformatted number. Here’s an example:


const number = 1000000;

const formattedNumber = number.toLocaleString();

console.log(formattedNumber); // Output: 1,000,000


The toLocaleString() method is straightforward to use, and you don’t need to specify anything about the format of the number.

JavaScript will automatically detect your machine’s conventions regarding formatting numbers. Formatting Numbers with Commas Using Regular Expressions with String.replace() Method

The String.replace() method is another built-in JavaScript function.

Regular expressions are a sequence of characters that defines a search pattern. Using this method, you can search for patterns in the number, such as commas, and replace them with nothing, or with an actual comma.

Here’s an example:


const number = 1000000;

const formattedNumber = number.toString().replace(/B(?=(d{3})+(?!d))/g, “,”);

console.log(formattedNumber); // Output: 1,000,000


In this example, we use the replace() method with a regular expression. The pattern we’re searching for is a sequence of three digits (d{3}) that aren’t preceded by a word boundary (B).

We replace this pattern with a comma and use the global flag (g) to replace all occurrences of the pattern.

Advantages of Using Regular Expressions over toLocaleString()

There are several advantages of using regular expressions over toLocaleString() when formatting numbers with commas.

Faster Performance

toLocaleString() is a built-in JavaScript method, so it’s commonly used by developers to format numbers with commas. However, when used to format large arrays of numbers, it can be very inefficient, causing performance issues.

Regular expressions, on the other hand, have faster performance, making them a better choice for large amounts of data.

Localizations and Country-Specific Formatting

toLocaleString() method formats numbers based on the user’s machine culture, which means it may not format numbers correctly in other regions. For example, in the US, the comma is used as a separator for every third digit in a number, but in other countries, such as France, the period is used instead of a comma.

Regular expressions, however, can format numbers specific to a particular country, making them more versatile.


Numbers are an essential part of programming, and formatting them correctly is crucial for optimal readability and comprehension. In this article, we have discussed two ways to format numbers with commas using JavaScript: toLocaleString() and Regular Expressions with String.replace().

While the toLocaleString() method is simple to use, regular expressions offer faster performance and the ability to format numbers based on specific regional conventions. Regardless of the method used, formatting numbers with commas is essential for clear, readable code.

In conclusion, formatting numbers with commas is a crucial step in writing readable and concise code. There are two main methods used in JavaScript to format numbers with commas: toLocaleString() and Regular Expressions with String.replace().

While toLocaleString() method is simple and widely used, Regular Expressions offer faster performance and the ability to format numbers based on specific regional conventions. By implementing these methods, developers can create code that is more efficient, flexible, and easier to read.

Remember, formatting numbers with commas may seem like a small detail, but it can make a significant difference in how well your code communicates its intent.

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