Polyfill import.meta.url when output format is cjs

[egoist]

This is the default behavior of Rollup so I think maybe esbuild should also add this 🤔

[evanw]

So esbuild generally doesn't do polyfills. It also doesn't polyfill node's built-in fs module, for example. Instead esbuild is generally only concerned about syntax features. This is broadly because syntax features are universal but the details of what polyfills you need or what they should do are specific to your situation. Instead esbuild provides general-purpose mechanisms that let you bring your own polyfills. For example:

$ cat import.meta.url-polyfill.js
export const import_meta_url =
  typeof document === 'undefined' ? new (require('url'.replace('', '')).URL)('file:' + __filename).href :
    (document.currentScript && document.currentScript.src || new URL('main.js', document.baseURI).href)

$ echo 'console.log(import.meta.url)' | esbuild --bundle --format=cjs --define:import.meta.url=import_meta_url --inject:./import.meta.url-polyfill.js | node
file:///[stdin]

You can read more about how to do this here: https://esbuild.github.io/api/#using-inject-with-define. Closing since I believe this to be out of scope.

[antongolub]

@evanw ,

new (require('url'.replace('', '')).URL or new (require('u' + 'rl').URL

Why do we need this trick?