A few days ago, Google released their Closure Compiler project for optimizing JavaScript. Here’s what they write about the Closure Compiler:

The Closure Compiler is a tool for making JavaScript download and run faster. It is a true compiler for JavaScript. Instead of compiling from a source language to machine code, it compiles from JavaScript to better JavaScript. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left.

The interesting part of the Closure Compiler is that it not only removes whitespace, it also rewrites your JavaScript code to make it smaller and optimizes the code for better performance. My tests show that it can reduce JavaScript files by about 60% - and that’s before HTTP compression! Considering how much JavaScript a modern website uses, this is no less than amazing and highly useful.

The Closure Compiler comes in two flavors – a Java based command line tool and a RESTful API. I’ve been playing around with the API and it works great and very fast.

The code

The C# class I’ve written takes a JavaScript file and passes it through the API and then returns the compressed JavaScript as a string. The class contains one public and one private method and is only 47 lines of code including 16 lines of comments.

public string Compress(string file)


  string source = File.ReadAllText(file);

  XmlDocument xml = CallApi(source);

  return xml.SelectSingleNode("//compiledCode").InnerText;



private static XmlDocument CallApi(string source)


  using (WebClient client = new WebClient())


    client.Headers.Add("content-type", "application/x-www-form-urlencoded");

    string data = string.Format(PostData, HttpUtility.UrlEncode(source));

    string result = client.UploadString(ApiEndpoint, data);


    XmlDocument doc = new XmlDocument();


    return doc;



How to use it

You can use the class to do various cool things. You can write a MSBuild or NAnt script that automatically compresses your JavaScript files as part of a continuous integration process or, as I prefer, write a HTTP handler to do the same but at runtime. Remember to output cache the compressed result. Here's an example of using the class from ASP.NET:

GoogleClosure gc = new GoogleClosure();

string script = gc.Compress(Server.MapPath("~/script.js"));

Remember that the class doesn't do any exception handling, so you might want to stick that in yourself.


GoogleClosure.zip (905,00 bytes)