Error while creating a web bundle with esbuild about level

[vweevers]

This can be "fixed" by adding external: ['events'] in the esbuild configuration, but that's probably a workaround.

That's the correct fix. As it stands, level is for Node.js first, browsers second. Bundlers should (be configured to) inject shims for Node.js core modules. Whether it's browserify (see browserify-starter), webpack (see webpack-starter/webpack.config.js), esbuild or other.

[ERROR] Transforming async generator functions to the configured target environment ("chrome58", "es2020", "firefox57", "safari11") is not supported yet

Safari < 12 is not supported by level because it doesn't support async generators (see caniuse).