js2coffee/notes/New_in_2.0.md

JavaScript to CoffeeScript compiler

# What's new in 2.0

**[Js2coffee] 2.0** is a complete rewrite of js2coffee v0.3 started in 2014. It was
released February 1, 2015 and features a new parser, [Esprima], replacing the
aging Narcissus build that has been in use since 2011.

----

## New web editor

![](http://js2.coffee/assets/screenshots/js2coffee.png)

The editor has been rebuilt and redesigned. It now features a new easy-to-use
editor based on [CodeMirror].

It also now lives in a new URL, [js2.coffee](http://js2.coffee), migrating away
from the old `js2coffee.org`.

----

## Warnings and errors

![](http://js2.coffee/assets/screenshots/warnings.png)

Constructs that are not available in CoffeeScript are marked with errors, such as:

 * Reassignment of global variables
 * `==` and `!=` operators
 * Variable shadowing

See this
[demo](http://js2.coffee/#try:alert%28function%20namedExpr%28%29{}%29%3B%0A%0Afunction%20fn%28%29%20{%0A%20%20if%20%28a%20%3D%3D%20b%29%20{%0A%20%20%20%20a%20%3D%20false%3B%0A%20%20}%0A})
for a few more.

----

## AST mode

![](http://js2.coffee/assets/screenshots/ast.png)

The js2coffee compiler now produces a CoffeeScript AST (abstract syntax tree) before
rendering your input into code. The command-line client features an `--ast`
mode which lets you inspect the generated CoffeeScript AST.

----

## Source maps

Source maps are now generated. More info on this soon.

----

## Compatibility mode

Js2coffee now features a *compatibility mode* (`--compat`) to improve
reliability over generated CoffeeScript code (at the slight expense of elegance).
see the [Compatibility mode] documentation.

Try this
[demo](http://js2.coffee/#try:alert%28function%20cube%28n%29{%0A%20%20return%20Math.pow%28n%2C%203%29%3B%0A}%29%3B)
— toggle the *compatibility mode* checkbox and see what happens.

----

## Improved API

The API has remained largely compatible with the 0.x series, but with
improvements. The JavaScript API also reports the AST tree, source maps and
warnings along with the output code. See the [Migration guide] for info on how
the API has changed.

### Tons of bugfixes

The 2.0 release closes a [lot of bugs][issues], including:

 * `npm install js2coffee` not working ([#324])
 * Empty if statements fail ([#265])
 * Variable scoping issues ([#219])
 * and many [more][issues]

----

## Linking and sharing

![](http://js2.coffee/assets/screenshots/linking.png)

You can show share your JavaScript and CoffeeScript snippets—perfect for
collaborating with coworkers or answering at StackOverflow.

----

## CoffeeScript preview pane

![](http://js2.coffee/assets/screenshots/preview.png)

The new [js2.coffee][Js2coffee] features an improved CoffeeScript to JavaScript
compilation UI. This makes it easier to see how Js2coffee-generated
CoffeeScript looks like compared to your original code.

[Esprima]: http://esprima.org/
[CodeMirror]: http://codemirror.net/
[issues]: https://github.com/js2coffee/js2coffee/issues?q=label%3A%22fixed+in+2.0%22+is%3Aclosed
[Js2coffee]: http://js2.coffee/
[Migration guide]: https://github.com/js2coffee/js2coffee/blob/master/notes/Migration_guide.md
[Compatibility mode]: https://github.com/js2coffee/js2coffee/blob/master/notes/Special_cases.md#compatibilitymode
[#324]: https://github.com/js2coffee/js2coffee/issues/324
[#265]: https://github.com/js2coffee/js2coffee/issues/265
[#219]: https://github.com/js2coffee/js2coffee/issues/219