The @eth-optimism/sdk package provides a set of tools for interacting with Optimism.
npm install @eth-optimism/sdk
You can find auto-generated API documentation over at sdk.optimism.io.
The CrossChainMessenger class simplifies the process of moving assets and data between Ethereum and Optimism.
You can use this class to, for example, initiate a withdrawal of ERC20 tokens from Optimism back to Ethereum, accurately track when the withdrawal is ready to be finalized on Ethereum, and execute the finalization transaction after the challenge period has elapsed.
The CrossChainMessenger can handle deposits and withdrawals of ETH and any ERC20-compatible token.
Detailed API descriptions can be found at sdk.optimism.io.
The CrossChainMessenger automatically connects to all relevant contracts so complex configuration is not necessary.
The Optimism SDK includes various utilities for handling Optimism's transaction fee model.
For instance, estimateTotalGasCost will estimate the total cost (in wei) to send at transaction on Optimism including both the L2 execution cost and the L1 data cost.
You can also use the asL2Provider function to wrap an ethers Provider object into an L2Provider which will have all of these helper functions attached.
The SDK contains other useful helper functions and constants. For a complete list, refer to the auto-generated SDK documentation