Starting as an option in Haxe 2.09, and as default in Haxe 3, the JS output is modernized, meaning:

• Output runs in ES5 strict mode, allowing for more robust and optimizable JS.

• Output is wrapped in a (function() {})() to prevent writing to the global namespace, and allow JS minifiers to be more efficient. You can intentionally write classes and static methods to the global namespace by tagging them with @:expose:
  

  @:expose("someLib.SomeName")
  class MyExternalClass { }

  
  Where "someLib.SomeName" is the optional exposed location of the class or function. By default, @:expose uses the full class and package name for the exposed location.

Haxe 3+

• Modern JS output mode is the default
• Enable Classic JS mode with -D js-classic

Haxe 2.09+

• Classic JS output remains the default
• Enable Modern JS output mode with --js-modern