About 
Improved JavaScript editing mode for GNU Emacs (description here).
For some of the latest changes, see latest user-visible changes.
Installation
The stable versions are hosted at GNU ELPA (M-x list-packages).
You can also install the latest development version from Melpa.
Emacs 22 and 23
This version requires Emacs 24. For a backward compatible version, check out the branch emacs23.
Bugs
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See broken syntax highlighting and timer errors? Recently upgraded Emacs from version 24.2 or earlier?
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Try reinstalling or byte-recompiling the package.
Please report problems at http://github.com/mooz/js2-mode/issues.
See Also
Some third-party modes that use the generated syntax tree: