YUI Compressor’s variable replacement functionality can give big byte savings while minifying your JavaScript. Since the YUI Compressor tries to avoid breaking your code by incorrectly replacing variable names, it will turn off variable replacement when the eval() function or with statement is used. These “evil” features alter how JavaScript code is interpreted and prevent the YUI Compressor from safely replacing variable names, which costs you a large amount of byte savings. Avoid this penalty by steering clear of eval() or sequester it away from the rest of your code. Also, avoid the with statement. These steps will ensure that your code doesn’t get in the way of optimal minification.