Include JS from ruby gem with esbuild

application.js

import "my-gem"

esbuild.config.js

require("esbuild").build({
  //...
  nodePaths: [process.env.NODE_PATH]
}).catch(() => process.exit(1));

package.json

//...
"scripts": {
    "build": "NODE_PATH=$(bundle show --paths my-gem)/app/javascript node esbuild.config.js"
}

Configuration for including javascript direct from a gem with esbuild as commonly found in Rail

To avoid ambiguity put the gem's js under a name-specific folder in app/javascript

e.g.

app/javascript/my-gem/index.js