Decimal.js — Arbitrary-Precision Decimal Arithmetic for JavaScript

Introduction

Decimal.js provides an arbitrary-precision Decimal type for JavaScript. It solves the classic IEEE 754 floating-point problem (0.1 + 0.2 !== 0.3) by representing numbers as decimal strings internally. It supports all standard arithmetic operations, trigonometric functions, and configurable precision up to millions of digits.

What Decimal.js Does

• Performs exact decimal arithmetic without floating-point rounding errors
• Supports configurable precision from 1 to millions of significant digits
• Provides sqrt, pow, log, exp, sin, cos, tan, and other transcendental functions
• Handles very large and very small numbers beyond Number.MAX_SAFE_INTEGER
• Returns Decimal objects that chain naturally for complex calculations

Architecture Overview

Decimal.js stores each number as an array of digits with a sign and exponent. Arithmetic operations use classical algorithms (long multiplication, Newton-Raphson for division and roots). The library is self-contained with no dependencies. A configurable global Decimal constructor lets you set precision, rounding mode, and other defaults.

Self-Hosting & Configuration

• Install via npm or include a single script file from a CDN
• Set global precision with Decimal.set({ precision: 50 })
• Choose from 9 rounding modes (ROUND_UP, ROUND_DOWN, ROUND_HALF_EVEN, etc.)
• Configure toExpPos and toExpNeg to control when exponential notation is used
• Zero dependencies; works in Node.js, Deno, and all browsers

Key Features

• Eliminates floating-point errors for financial and scientific calculations
• Configurable precision up to 1 billion significant digits
• Full suite of mathematical functions including trigonometry and logarithms
• Immutable Decimal instances prevent accidental mutation
• Comprehensive test suite with thousands of test cases

Comparison with Similar Tools

• big.js — Simpler API for basic arithmetic; Decimal.js adds trig and log functions
• bignumber.js — Same author; Decimal.js uses a different internal format and adds more math functions
• mathjs — Full math library; Decimal.js is focused purely on arbitrary precision numbers
• Native BigInt — Integers only; Decimal.js handles fractional values

FAQ

Q: When should I use Decimal.js over native numbers? A: Use it when exact decimal representation matters: finance, currency, scientific computation.

Q: How fast is it compared to native arithmetic? A: Slower than native floats, but optimized for its class. Most operations complete in microseconds.

Q: What is the difference between decimal.js, big.js, and bignumber.js? A: All three are by the same author. Decimal.js has the most features; big.js is the smallest; bignumber.js is in between.

Q: Does it support serialization? A: Yes, toString() and toJSON() produce string representations that can reconstruct Decimal instances.

Sources

• https://github.com/MikeMcl/decimal.js
• https://mikemcl.github.io/decimal.js/