All you need to know about BigInt in JavaScript

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Last updated: October 7, 2021.

Until ECMAScript 2020 (ES11), JavaScript consisted of six ‘primitive’ data types:

  • Number
  • String
  • Boolean
  • Null
  • Undefined
  • Symbol

Primitive types are the most basic possible data in JavaScript, i.e. they cannot be reduced to a more basic type.

With ECMAScript 2020, a seventh primitive type was introduced to the language to the language, BigInt.

In this article, we will cover all you need to know about BigInt: Why we need it, how to create it and features of working with it.

Let’s get started!

Why we need BigInt

It may surprise you, but JavaScript’s Number type isn’t perfect at handling very large numbers with precision.

In fact, by calling Number.MAX_SAFE_INTEGER, we can see the largest integer that it is safe to work with when working with Number data:

alert(Number.MAX_SAFE_INTEGER); // 9007199254740991

This implies that working with numbers in excess of this is ‘unsafe’. What do we mean?

Concretely, we can work with an integer of type Number up until 9007199254740991 with guaranteed precision. But working with numbers greater than this risks losing precision.

For example, if we try to alert the number 99999999999999999 as a Number type, you can clearly see the problem:

alert(99999999999999999); // 100000000000000000

This makes exact calculations with very large numbers problematic when using the Number type. It can also be a problem if the number is long but needs to be exact, such as an identification or serial number.

BigInt enables us to work with larger numbers without losing any precision.

Creating a BigInt

BigInt is a built-in JavaScript object that can be called to create a new BigInt integer.

The first way to create a BigInt integer is to call the object directly. For example:

const largeNumber = BigInt("99999999999999999");
console.log(largeNumber); // 99999999999999999n
console.log(typeof largeNumber); // bigint

A more convenient method is to simply place n after a number:

const largeNumber = 99999999999999999n;
console.log(largeNumber); // 99999999999999999n
console.log(typeof largeNumber), // bigint

BigInt features

BigInt can handle smaller numbers to, just like Number.

const x = BigInt("2");
console.log(x); // 2n

To distinguish BigInt from Number, n is returned after the interger.

BigInt and Number types cannot be mixed in a calculation. If you try to do so, JavaScript will return an error:

const x = BigInt("2");
const y = 2
console.log(x + y); // Uncaught TypeError: Cannot mix BigInt and other types, use explicit conversions

If we want to make such a calculation, we can by convert the Number to a BigInt by passing it inside BigInt():

const x = BigInt("2");
const y = 2;
console.log(x + BigInt(y)); // 4n

Or, by converting the BigInt value to a Number type by passing it through Number():

const x = BigInt("2");
const y = 2;
console.log(Number(x) + y); // 4

When making comparisons, if BigInt and Number contain the same value, they are considered equal (==) but not strictly equal (===):

const x = BigInt("2");
const y = 2;

alert(x==y); // true
alert(x===y); // false

Summary

In this article, we have seen why we need BigInt, how to create one and its most important features.

It is not a primitive data type that you will use anywhere near as much as Number, String or Boolean. However, it is a welcome addition that increases the reliability of the language.