How Should We Handle Precision Issues in JavaScript?

JavaScript's native Number type is a 64-bit floating point number (IEEE 754). This limits its integer precision to 2^53 - 1, or about 9e15. Beyond that, numbers get rounded and lose accuracy.

console.log(Number.MAX_SAFE_INTEGER); // 9007199254740991
console.log(9007199254740991 + 1);    // 9007199254740992 ✅
console.log(9007199254740991 + 2);    // 9007199254740992 ❌ precision loss

• Ethereum (and other EVM chains) use wei as the smallest unit of ETH.

• 1 ETH = 10^18 wei → sending just 1 ETH involves manipulating a big integer, far beyond JS safe integer range.

• Smart contracts return values in wei, making it unsafe to use regular Number for balances, gas, token supply, etc.

To safely handle large numbers in Web3 apps, you must use arbitrary-precision number types, like:

• ethers.BigNumber (from ethers.js)

• BigNumber.js (arbitrary precision lib)

• Native BigInt (ES2020)

• web3.utils.BN (if using web3.js)

Example (using ethers.js):

import { parseEther, formatEther } from 'ethers'; 
const amountInWei = parseEther('1.0'); // returns BigNumber of 10^18 console.log(amountInWei.toString()); // '1000000000000000000' 
const readable = formatEther(amountInWei); // back to human-readable ETH console.log(readable); // '1.0'

Avoid this unless you're 100% sure the value is within the safe range:

const unsafe = BigNumber.from("1000000000000000000"); console.log(unsafe.toNumber()); // May throw or round incorrectly if too large

Instead, use:

console.log(unsafe.toString()); // Safe

If you don’t need compatibility with libraries like ethers.js, and you’re just doing arithmetic:

const a = BigInt("1000000000000000000"); 
const b = BigInt("3000000000000000000"); 
const c = a + b; 
console.log(c.toString()); // "4000000000000000000"

But be careful: BigInt ≠ Number, and you can’t mix them.

ReasonExplanation✅ PrecisionJS Number can't represent large wei values accurately💡 CompatibilityWeb3 libraries return balances and values as BigNumber🔒 SafetyPrevent silent rounding bugs in balances, gas, etc.🛠️ ToolsUse parseEther, formatUnits, BigNumber.from, etc.

How Should We Handle Precision Issues in JavaScript?

JavaScript's native Number type is a 64-bit floating point number (IEEE 754). This limits its integer precision to 2^53 - 1, or about 9e15. Beyond that, numbers get rounded and lose accuracy.

console.log(Number.MAX_SAFE_INTEGER); // 9007199254740991
console.log(9007199254740991 + 1);    // 9007199254740992 ✅
console.log(9007199254740991 + 2);    // 9007199254740992 ❌ precision loss

• Ethereum (and other EVM chains) use wei as the smallest unit of ETH.

• 1 ETH = 10^18 wei → sending just 1 ETH involves manipulating a big integer, far beyond JS safe integer range.

• Smart contracts return values in wei, making it unsafe to use regular Number for balances, gas, token supply, etc.

To safely handle large numbers in Web3 apps, you must use arbitrary-precision number types, like:

• ethers.BigNumber (from ethers.js)

• BigNumber.js (arbitrary precision lib)

• Native BigInt (ES2020)

• web3.utils.BN (if using web3.js)

Example (using ethers.js):

import { parseEther, formatEther } from 'ethers'; 
const amountInWei = parseEther('1.0'); // returns BigNumber of 10^18 console.log(amountInWei.toString()); // '1000000000000000000' 
const readable = formatEther(amountInWei); // back to human-readable ETH console.log(readable); // '1.0'

Avoid this unless you're 100% sure the value is within the safe range:

const unsafe = BigNumber.from("1000000000000000000"); console.log(unsafe.toNumber()); // May throw or round incorrectly if too large

Instead, use:

console.log(unsafe.toString()); // Safe

If you don’t need compatibility with libraries like ethers.js, and you’re just doing arithmetic:

const a = BigInt("1000000000000000000"); 
const b = BigInt("3000000000000000000"); 
const c = a + b; 
console.log(c.toString()); // "4000000000000000000"

But be careful: BigInt ≠ Number, and you can’t mix them.

ReasonExplanation✅ PrecisionJS Number can't represent large wei values accurately💡 CompatibilityWeb3 libraries return balances and values as BigNumber🔒 SafetyPrevent silent rounding bugs in balances, gas, etc.🛠️ ToolsUse parseEther, formatUnits, BigNumber.from, etc.