The dart.js file is used in Dart browser apps to check for native Dart support and either (a) bootstrap Dartium or (b) load compiled JS instead. Previously, we've recommended that you add a script tag pointing the version of dart.js in our repository. This doesn't work offline and also results in slower startup (see dartbug.com/6723).
Instead, we now recommend that you install dart.js via the following steps:
Add the following to your pubspec.yaml: dependencies: browser: any
Run pub install.
Use a relative script tag in your html to the installed version:
If you do not wish to use pub, you may host a copy of this file locally instead. In this case, you will need to update it yourself as necessary. We reserve the right to move the old file in the repository, so we no longer recommend linking to it directly.