Numbers in JavaScript are stored in double-precision 64-bit binary
format IEEE 754. Like any other number encoding occupying a finite number of bits, it is unable to represent all numbers.
The values are stored using 64 bits in the following form:
- 1 bit for the sign (positive or negative)
- 11 bits for the exponent (2n). -1022 ≤ n ≤ 1023
- 52 bits for the significand (or mantissa)
The actual value of the stored number will be (-1)sign * (1 + significand) * 2 exponent
Given this structure, there are limits in both magnitude and precision.
Due to the 52 bits used for the significand, any arithmetic in need of more precision than 2-52 (provided by
Number.EPSILON) is subject to rounding.
In terms of magnitude, the largest number the 64 bits of the format can store is 21024 - 1 (Number.MAX_VALUE).
However, because the 52 bits of the significand, only integers between -(253 - 1) (Number.MIN_SAFE_INTEGER) and
253 - 1 (Number.MAX_SAFE_INTEGER) can be represented exactly and be properly compared.
Number.MAX_SAFE_INTEGER + 1 === Number.MAX_SAFE_INTEGER + 2; // true
JavaScript provides the bigint primitive to represent values which are too large to be represented by the number primitive. BigInts
are created by appending n to the end of an integer literal, or by calling the BigInt() function (without the new operator),
with an integer or a string.
const myBigInt = BigInt(Number.MAX_SAFE_INTEGER);
myBigInt + 1n === myBigInt + 2n; // false
