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JavaScript Numbers
JavaScript has only one type of number. Numbers can be written with or without decimals.
Example
let x = 3.14; // A number with
decimals
let y = 3; // A number without decimals
Extra large or extra small numbers can be written with scientific (exponent) notation:
Example
let x = 123e5;
// 12300000
let y = 123e-5; // 0.00123
JavaScript Numbers are Always 64-bit Floating Point
Unlike many other programming languages, JavaScript does not define different types of numbers, like integers, short, long, floating-point etc.
JavaScript numbers are always stored as double precision floating point
numbers, following the international IEEE 754 standard.
This format
stores numbers in 64 bits, where the number (the fraction) is stored in bits 0
to 51, the exponent in bits 52 to 62, and the sign in bit 63:
| Value (aka Fraction/Mantissa) | Exponent | Sign |
|---|---|---|
| 52 bits (0 - 51) | 11 bits (52 - 62) | 1 bit (63) |
Precision
Integers (numbers without a period or exponent notation) are accurate up to 15 digits.
Example
let x = 999999999999999;
// x will be
999999999999999
let y = 9999999999999999; // y will be 10000000000000000
The maximum number of decimals is 17, but floating point arithmetic is not always 100% accurate:
Example
let x = 0.2 + 0.1;
// x will be 0.30000000000000004
To solve the problem above, it helps to multiply and divide:
Example
let x = (0.2 * 10 + 0.1 * 10) / 10; // x will be 0.3