# Automating ethers.js v5 v6 Migration with Codemods

Deewakar Bora — Sun, 12 Apr 2026 17:00:15 +0000

Ethers.js v5 has dozens of breaking changes when upgrading to v6. BigNumber is gone, provider names changed, utility functions moved, and contract patterns restructured. Doing this by hand across hundreds of files takes days.
I built a codemod toolkit using jssg (JavaScript ast-grep) that automates 95% of this migration with one command.

Quick Start

npx codemod ethers-v5-to-v6-codemod

The Problem

Thousands of DeFi projects are still on ethers v5. The migration is painful not because any single change is hard, but because of sheer volume across hundreds of files. Simple regex fails on edge cases. The ecosystem needed a structural solution.

The Approach

12 jssg (JavaScript ast-grep) transforms orchestrated via workflow.yaml. jssg parses code into an AST — so replacements are structurally exact and never touch patterns inside string literals or comments. Zero false positives guaranteed.

What Gets Automated

Utils functions — ethers.utils.formatEther, parseEther, formatUnits, arrayify, hexlify, and 10 more
BigNumber to BigInt — BigNumber.from(x) to BigInt(x) with smart scope-aware detection
Provider renames — ethers.providers.Web3Provider to ethers.BrowserProvider
Crypto utils — keccak256, sha256, toUtf8Bytes, solidityKeccak256
callStatic to staticCall — contract.callStatic.foo() to contract.foo.staticCall()
Contract address — contract.address to contract.target
Broadcast transaction — provider.sendTransaction(hex) to provider.broadcastTransaction(hex)
Signature class — splitSignature, joinSignature, verifyMessage, recoverAddress
Import cleanup — removes deprecated BigNumber and providers imports
Gas price — provider.getGasPrice() to provider.getFeeData()
Contract methods — estimateGas, populateTransaction, functions namespace
Sub-package imports — @ethersproject/* to ethers

Real World Proof

Tested on thallo-io/ethers-js-cheatsheet — a real open source TypeScript DeFi project.
Result: 6 files transformed, 0 errors, 0 false positives, 1.266 seconds

Uniswap quote script before:

const amountIn = ethers.utils.parseEther("1");
const priceQuote = await uni.callStatic.quoteExactInputSingle(WETH9, DAI, fee, amountIn, sqrtPriceLimitX96);
console.log(ethers.utils.formatEther(priceQuote));

After:

const amountIn = ethers.parseEther("1");
const priceQuote = await uni.quoteExactInputSingle.staticCall(WETH9, DAI, fee, amountIn, sqrtPriceLimitX96);
console.log(ethers.formatEther(priceQuote));

Three patterns fixed automatically in one pass.

Coverage Breakdown

Automated by jssg transforms: ~95%
AI following AI-INSTRUCTIONS.md: ~4%
Manual review: ~1%

Forem: Deewakar Bora