FileInfo.coffee

class FileInfo
  constructor: (filename) ->
    @name = filename

  mtime: ->
    # in CoffeeScript, the last thing in a function is returned
    # which in this case is the value returned from @withFile
    # which is the value returned from the inner function
    # => binds scope to the correct `this`
    @withFile (f) =>
      mtime = @mtimeFor(f)
      return "too old" if mtime < Date.now() - 1000
      console.log "recent!"
      return mtime

  body: ->
    @withFile (f) =>
      return f.read()

  mtimeFor: (f) ->
    return File.mtime(f)

  withFile: (fn) ->
    try
      f = File.open(@name, "r")
      fn(f) # the result of this is implicitly returned in CoffeeScript
    finally
      f.close()

FileInfo.js

function FileInfo(filename) {
  this.name = filename;
}

FileInfo.prototype = {
  mtime: function() {
    // return the result of the inner function
    return this.withFile(function(f) {
      var mtime = this.mtimeFor(f);
      if (mtime < Date.now() - 1000) {
        return "too old";
      }
      console.log("recent!");
      return mtime;
    }.bind(this)); // bind scope
  },

  body: function() {
    return this.withFile(function(f) { return f.read(); });
  },

  mtimeFor: function(f) {
    return File.mtime(f);
  },

  withFile: function(fn) {
    try {
      var f = File.open(this.name, "r");
      return fn(f); // call and return the result of the "block"
    } finally {
      f.close();
    }
  }
};

It didn't take much work to get JS to perform as expected, a few extra return statements and a bind call and we're done. CoffeeScript is even closer with its implicit returns and => binding syntax. Am I missing something else, or do we already have everything we need and this is just sugar?