Integer vs Float

Precision and floating point arithmetic.

JavaScript numbers are always stored as double precision floating point numbers, following the international IEEE 754 standard.

Integers (numbers without a period or exponent notation) are accurate up to 15 digits.

Floating point arithmetic is not always 100% accurate.

let x = 0.2 + 0.1; // 0.30000000000000004

Example

let x = 999999999999999;   // x will be 999999999999999
let y = 9999999999999999;  // y will be 10000000000000000