Compiling CoffeeScript with Vim

You can configure Vim to automatically compile CoffeeScript files when you save them from within Vim, it’s easy, just add an autocmd to run the CoffeeScript compiler to your ~/.vimrc file:

autocmd BufWritePost,FileWritePost *.coffee silent !coffee -c <afile>

I prefer this to the CoffeeScript compiler --watch option because you get to see any compiler errors in the editor when you save the CoffeeScript source file.

In a similar vein the following two Vim auto-commands will compile Less and Stylus files to CSS:

autocmd BufWritePost,FileWritePost *.less silent !lessc <afile> <afile>:r.css
autocmd BufWritePost,FileWritePost *.styl silent !stylus <afile> >/dev/null

Tip: Use Ctrl+L to clear any compiler errors and redraw the screen or delete the silent option from the Vim autocmd.

This technique works, but what happens if you want to selectively include CoffeeScript compiler options with some files and not others? I came up against this problem writing QUnit tests using CoffeeScript which must be compiled without the top-level function wrapper using the --bare command-line option.

My solution was to take a cue from Vim’s mode line feature and write a CoffeeScript compiler wrapper shell script which scans the end of the CoffeeScript source file for a comment line starting with # coffee:, it then passes the remainder of the line to the CoffeeScript compiler as command-line options. Here’s a basic CoffeeScript QUnit test file specifying the --bare option in the trailing mode line:

module 'Test'

test 'addition', ->
    equals 1+1, 2, 'one and one is two'

# coffee: --bare

And here’s the coffee.sh wrapper script:

    #!/bin/sh
    #
    # 'Mode line' wrapper for CoffeeScript 'coffee' compiler command.
    #
    # Executes CoffeeScript compiler and includes compiler options from line at the
    # end of the CoffeeScript source file starting with '# coffee:' (c.f. Vim mode
    # lines).
    #
    
    # Last argument is the source file name.
    for srcfile; do true; done
    
    # Search the last 5 lines in the source for a mode line and extract the
    # trailing coffee command options.
    # Default to the --compile option.
    pat='^#\s*coffee:'
    opts=$(tail -n5 $srcfile | grep "$pat" | sed "/$pat/s/$pat//")
    opts=$(echo $opts | sed -r -e 's/^ *//' -e 's/ *$//')   # Trim spaces.
    if [ -z "$opts" ]; then
        opts="--compile"
    fi
    
    coffee $opts $@

You also need to change coffee to coffee.sh in your ~/.vimrc autocmd plus you need to ensure both coffee to coffee.sh are in your shell search PATH:

autocmd BufWritePost,FileWritePost *.coffee !coffee.sh -c <afile>

Tip: If you don’t want to generate a compiled JavaScript file (for example, Jake and Cake CoffeeScript files) use the --lint option:

# coffee: --lint