Here's an example of how to use Bundlr / Arweave with Lit.
1. You will need to have an Arweave wallet already, if not click here
2. You will need to fund the node (it might take up to an hour), more info here
1. Drop your wallet.json keyfile to login
It uses the FileReader API to read the file as text and pass it to the Bundlr constructor to get its wallet address