The most obvious way to get the address for a pair is to call getPair on the factory. If the pair exists, this function will return its address, else address(0) (0x0000000000000000000000000000000000000000).

• The "canonical" way to determine whether or not a pair exists.
• Requires an on-chain lookup.

CREATE2

Thanks to some fancy footwork in the factory, we can also compute pair addresses without any on-chain lookups because of CREATE2. The following values are required for this technique:

address	The factory address
salt	keccak256(abi.encodePacked(token0, token1))
keccak256(init_code)	0x96e8ac4277198ff8b6f785478aa9a39f403cb768dd02cbee326c3e7da348845f

• token0 must be strictly less than token1 by sort order.

• Can be computed offline.
• Requires the ability to perform keccak256.

Examples

TypeScript

This example makes use of the Pegasys SDK. In reality, the SDK computes pair addresses behind the scenes, obviating the need to compute them manually like this.

import { FACTORY_ADDRESS, INIT_CODE_HASH } from '@pollum-io/pegasys-sdk'

import { pack, keccak256 } from '@ethersproject/solidity'

import { getCreate2Address } from '@ethersproject/address'

const token0 = '0xCAFE000000000000000000000000000000000000' // change me!

const token1 = '0xF00D000000000000000000000000000000000000' // change me!

const pair = getCreate2Address(

FACTORY_ADDRESS,

keccak256(['bytes'], [pack(['address', 'address'], [token0, token1])]),

INIT_CODE_HASH

)