Migrating from big.js

big.js is the smallest of the three MikeMcl libraries. Moving to BigDecimal.js gives you the full Java BigDecimal surface (all eight rounding modes, engineering strings, Intl formatting) — with these differences:

1. No global Big.DP / Big.RM. big.js reads global decimal-places and rounding-mode for div/sqrt/round. Here you pass a scale + RoundingMode, or a MathContext, per call.
2. Java method names. plus → add, times → multiply, cmp → compareTo, neg → negate.
3. Eight rounding modes, not four — see Rounding Modes.
4. divide throws on non-terminating results unless given a scale or MathContext.

Method equivalents

big.js	BigDecimal.js
Big('1.5') / new Big('1.5')	Big('1.5') (with or without new)
x.plus(y)	x.add(y)
x.minus(y)	x.subtract(y)
x.times(y)	x.multiply(y)
x.div(y)	x.divide(y, scale?, roundingMode?)
x.mod(y)	x.remainder(y)
x.pow(n)	x.pow(n)
x.sqrt()	x.sqrt(mc) — MathContext required
x.abs()	x.abs()
x.neg()	x.negate()
x.round(dp, rm)	x.setScale(dp, roundingMode) or x.round(mc)
x.cmp(y)	x.compareTo(y)
x.eq(y)	x.sameValue(y) (value) or x.equals(y) (value + scale)
x.gt(y) / x.gte(y) / x.lt(y) / x.lte(y)	same names
x.toNumber()	x.numberValue()
x.toFixed(n) / x.toExponential(n) / x.toPrecision(n)	same names
Big.roundHalfUp (1)	RoundingMode.HALF_UP
Big.roundHalfEven (2)	RoundingMode.HALF_EVEN
Big.DP / Big.RM (globals)	per-call scale + RoundingMode, or MathContext

round → setScale

big.js round(dp, rm) becomes setScale(dp, roundingMode):

// big.js
new Big('2.345').round(2, Big.roundHalfUp) // 2.35

// BigDecimal.js
import { Big, RoundingMode } from 'bigdecimal.js'
Big('2.345').setScale(2, RoundingMode.HALF_UP).toString() // '2.35'

Global DP → explicit division

// big.js
Big.DP = 10
new Big(1).div(3) // 0.3333333333

// BigDecimal.js
Big(1).divide(3, 10, RoundingMode.HALF_UP).toString() // '0.3333333333'

Sign checks

big.js has no isZero/isNegative; you'd use cmp(0) or read .s. This library gives you predicates:

Big('0').isZero()      // true
Big('-3').isNegative() // true
Big('3').isPositive()  // true
Big('-3').signum()     // -1

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