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69 Chapter 10 CHAPTER 10 Rule 10: Minify JavaScript10 JavaScript, being an interpreted language, is great for building web pages. Inter- preted languages excel when developing user interfaces where rapid prototyping is the norm. Without a compilation step, though, the responsibility falls on the front- end engineer to optimize the JavaScript before final deployment. One aspect of this, gzipping, is discussed in Chapter 4. In this chapter, I describe another step that should be integrated into the JavaScript deployment process: minification. Minification Minification is the practice of removing unnecessary characters from code to reduce its size, thereby improving load times. When code is minified, all comments are removed, as well as unneeded whitespace characters (space, newline, and tab). In the case of JavaScript, this improves response time performance because the size of the downloaded file is reduced. Table 10-1 shows how many of the 10 top U.S. web sites practice JavaScript minifi- cation— 4 out of 10 minify their JavaScript code. Table 10-1. Minification practices across 10 top web sites Web site External scripts minified? http://www.amazon.com/ No http://www.aol.com/ No http://www.cnn.com/ No http://www.ebay.com/ Yes http://froogle.google.com/ Yes http://www.msn.com/ Yes http://www.myspace.com/ No http://www.wikipedia.org/ No http://www.yahoo.com/ Yes http://www.youtube.com/ No