Buffer.getMode returns the ace mode based on the url.

spec/atom/buffer-spec.coffee

@@ -45,5 +45,13 @@ describe 'Buffer', ->
         buffer = new Buffer
         expect(-> buffer.save()).toThrow()
 
+  describe "getMode", ->
+    describe "when given a url", ->
+      it "sets 'mode' based on the file extension", ->
+        buffer = new Buffer 'something.js'
+        expect(buffer.getMode().name).toBe 'javascript'
 
-
+    describe "when no url is given", ->
+      it "sets 'mode' to text mode", ->
+        buffer = new Buffer 'something'
+        expect(buffer.getMode().name).toBe 'text'

src/atom/buffer.coffee

@@ -11,6 +11,7 @@ class Buffer
       fs.read(@url)
     else
       ""
+
     @aceDocument = new Document text
 
   getText: ->
@@ -19,6 +20,18 @@ class Buffer
   setText: (text) ->
     @aceDocument.setValue text
 
+  getMode: ->
+    return @mode if @mode
+
+    extension = @url.split('/').pop().split('.').pop()
+    modeName = switch extension
+      when "js" then "javascript"
+      else "text"
+
+    @mode = new (require("ace/mode/#{modeName}").Mode)
+    @mode.name = modeName
+    @mode
+
   save: ->
     if not @url then throw new Error("Tried to save buffer with no url")
     fs.write @url, @getText()