Which files are generated when executing `dart2js`? and why?

dart2js probably generates .js.map, .js.deps and .precompiled.js.

What's the purpose of them? and I donno why dart2js doens't remove them after finishing compile.

All files are generated by dart2js on purpose:

.js: The JavaScript output of your application

.precompiled.js: The JavaScript output but with content security policy (CSP) support

.js.map: source map file used for debugging the JavaScript code in the browser. It contains a mapping from JavaScript to Dart code lines.

.js.deps: contains a list list of all references files used for compilation, prop ably for debugging but I'm not sure about this.

Here is what I believe is correct at the time I write this:

.js - the main JavaScript output of dart2js

Convention is to us the -o option to set the generated Javascript filename to end with .dart.js to differentiate generated Javascript from explicit Javascript in the Dart project. E.g.:

dart2js -o main.dart.js main.dart

pub-build does that by default. The dart.js file assumes this convention is used. Sample Dart .gitignore files often include *.dart.js.
.js.map - provides source maps from JavaScript to Dart that make debugging easier
.js.deps - what files were used when compiling with dart2js
.info.json - json file with information about the generated code (if --dump-info specified)
.js_1.part.js, .js_2.part.js etc. - parts of deferred imports

Sample Dart .gitignore files often include *.js_ to cover these files.
The --deferred-map option will generate a json file that you must provide a file name for.
.precompiled.js is no longer produced by dart2js

See:

https://www.dartlang.org/tools/private-files.html
https://github.com/dart-lang/www.dartlang.org/issues/1496 for my conversation with the site authors on making some adjustments.
https://www.dartlang.org/tools/dart2js/
https://github.com/github/gitignore/blob/master/Dart.gitignore.

来源：https://stackoverflow.com/questions/20314796/which-files-are-generated-when-executing-dart2js-and-why

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