Learn BigInt in JavaScript

Learn how to use BigInt in JavaScript to store large numbers

BigInt is a built-in object that provides a way to store numbers larger than Number.MAX_SAFE_INTEGER.

The reason for the need of BigInt is

var maxIntNum = 9007199254740991;

var largeNumber = maxIntNum + 2; // 9007199254740992

The expected result for the above operation is 9007199254740993, but we get 9007199254740992. The reason is that JavaScript uses 64 bits to store a number, so once we try to create a number larger than this, it can’t be stored.

To solve this problem, we can go for BigInt.

Creating BigInt

1. Adding n to end of a number

var num =  100000000000000000n;

num  + 10n;  // 100000000000000010n

// using binary literal with n appended

var num = 0x1fffffffffffffn

num; // 9007199254740991n

2. Using the BigInt constructor

var num = BigInt(100000000000000000);

num+10n; //100000000000000010n

var fromHex = BigInt('0x1fffffffffffff');

fromHex; // 9007199254740991n

Converting a BigInt to an object

var bigIntAsObject = Object(1n);

bigIntAsObject; // BigInt {1n}

Check if a number is a BigInt

typeof num === "bigint";

typeof bigIntAsObject; "object"

Remember, we cannot mix normal numbers with BitInt, and if we try to, it results in an error.

num + 10;

// Uncaught TypeError: Cannot mix BigInt and other types, use explicit conversions

To solve this, we can do the following by converting our normal number to a BigInt:

num + BigInt(10);

Arithmetic operations with BigInt

var num = BigInt(10);

Addition
num + 10n; // 20n

Subtraction
num - BigInt(5); // 15n

Multiplication 
num * 10n; // 150n

Exponent operator 
num ** 10n; // 10000000000n

DIVISION

// when we perform division , the fractional part in the result is removed

var n  = 5n;
n / 2n;  // 2n

MODULO

var n  = 5n;
n % 2n; // 1n

Equality Comparison

10n == 10; // true

When BigInt is compared with non-BigInt numbers, using strict-equality === always results in false.

10n === 10; // false

Relational Operations

It is similar to number comparisons

1n < 2
// true

2n > 1
// true

2 > 2
// false

2n > 2
// false

2n >= 2
// true

Converting to Boolean

Boolean(0n) // false

Boolean(12n) // true

!0n; // true

!12n; // false.

Parsing with JSON

var n = 100n;

JSON.stringify(n); 
// Uncaught TypeError: Do not know how to serialize a BigInt

Methods

toString

The toString method of BigInt will return a string representing the specified BigInt object without n at the end of the number.

var a = 10n;

a.toString(); //10

We can use the toString() method to solve errors caused by the stringify method. To solve this, we will add the toJSON method to the BigInt prototype.

BigInt.prototype.toJSON = function() {

    return this.toString();

}

valueOf

The valueOf() method returns the wrapped primitive value of a BigInt object.

var obj = Object(10n);

obj.valueOf(); // 10n

Reference: MDN

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