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Side-effect-free helpers for building ERC-20 calls and looking up tokens. Pair them with custom for ergonomic custom calldata. 
import { parseUnits } from 'viem'
import {
  erc20Utils,
  buildCall,
  buildApproveAndCall,
  buildErc20Approve,
  getAmountWithSlippage,
} from '0xtrails'

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Token registry — erc20Utils

Look up canonical token metadata (address + decimals) per chain. 
erc20Utils.USDC.onChain('base')
// → { address: "0x833…", decimals: 6, name: "USD Coin", imageUrl: "…" }

erc20Utils.USDC.addressOn('base')
erc20Utils.USDC.decimalsOn('base')

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Generic symbol lookup

For symbols not pinned as top-level properties: 
erc20Utils.token('WETH').onChain(42161)

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ERC-20 calldata builders

Standard calls, amounts are raw bigint wei: 
const amount = parseUnits('1', 6) // 1 USDC

erc20Utils.approve({ tokenAddress, spender, amount })
erc20Utils.transfer({ tokenAddress, to, amount })
erc20Utils.transferFrom({ tokenAddress, from, to, amount })
Each returns a Call. To include one in an action list, spread it into custom({ ...call }): 
import { custom, erc20Utils } from '0xtrails'
import { parseUnits } from 'viem'

custom({
  ...erc20Utils.approve({
    tokenAddress: erc20Utils.USDC.addressOn('base'),
    spender: '0xMyContract…',
    amount: parseUnits('100', 6),
  }),
})

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Composing calls — buildCall / buildApproveAndCall

buildCall constructs a Call from an ABI + function name + args: 
import { buildCall } from '0xtrails'

const stake = buildCall({
  to: STAKING_CONTRACT,
  data: {
    abi: stakingAbi,
    functionName: 'stake',
    args: [parseUnits('100', 6)],
  },
})
buildApproveAndCall bundles an approval and a follow-up call into a [approve, call] tuple: 
import { buildApproveAndCall, erc20Utils } from '0xtrails'

const [approve, stakeCall] = buildApproveAndCall({
  token: erc20Utils.USDC.addressOn('base'),
  call: stake,
  // amount defaults to maxUint256
})

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Slippage helper — getAmountWithSlippage

Subtracts bps basis points (1 bp = 0.01%) from a raw bigint amount. 
getAmountWithSlippage(parseUnits('1', 6), 50) // 1 USDC, 0.5% → 0.995 USDC
getAmountWithSlippage(parseUnits('1', 6), 500) // 1 USDC, 5%  → 0.95 USDC
Handy for computing a safe minAmountOut or amountOutMinimum before handing it to swap or the chain-scoped Uniswap V3 / SushiSwap V3 adapters.