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What is a BigInt in JavaScript?

Programming Bytes

BigInt

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

Take a look at the example below to see why BigInt is needed.

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 use a BigInt.

Creating a BigInt

We can create a BigInt in two ways:

  • Adding n to the end of the number.
  • Using the BigInt constructor.
// add n to end of the number to create a BigInt

var num =  100000000000000000n;
num  + 10n;  // 100000000000000010n

// creating BigInt from hexadecimal literal - append n at the end 
var num = 0x1fffffffffffffn
num; // 9007199254740991n

// using BigInt constuctor
var num = BigInt(100000000000000000);
num+10n; //100000000000000010n

var fromHex = BigInt('0x1fffffffffffff');
fromHex; // 9007199254740991n

Checking if a number is a BigInt

typeof will return bigint for BigInt numbers.

var num =  100000000000000000n;
typeof num; // bigint
var num2 = BigInt(100000000000000000);
typeof num2; // bigint

Creating an Object from a BigInt

We can create an object from a BigInt value, the type of which will be object.

var bigIntAsObject = Object(1n);
bigIntAsObject; // BigInt {1n}

typeof bigIntAsObject; // "object"

Remember, we cannot mix normal numbers with BigInts. If we try to, it will result in an error.

num + 10;
// Uncaught TypeError: Cannot mix BigInt and other types, use explicit conversions

To solve this, we can convert our normal number to a BigInt with the following.

num + BigInt(10);

Arithmetic operations with BigInt

Arithmetic operation on BigInt is mostly like arithmetic operation on regular numbers. However, when we perform division, the fractional part in the result is removed.

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

When BigInt is compared with non-BigInt numbers, will perform type conversion and check, using == but strict-equality === type conversion is not performed and returns false if values and types are not matched.

10n == 10; // true
10n === 10; // false

Relational operations

These are similar to numerical comparisons.

1n < 2n // true

2n > 1n // true

2 > 2n // false

2n > 2n // false

2n >= 2n // true

Converting to a Boolean

BigInts behave like numbers when converting to booleans or checking for true or false values.

Boolean(0n) // false
Boolean(12n) // true
!0n; // true
!12n; // false.


toString

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

var a = 10n;
a.toString(); //10

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