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We've grown into a very impatient societya culture of survival of the fastest. Waiting is not an option any more. Search engines like Google, Bing, and Yahoo are competing to offer the fastest and best search results. Ecommerce sites like Amazon, Target and Walmart are competing with innovative delivery methods like same-day delivery drones. And our everyday life is increasingly moving towards an online life, where slowness is not acceptable. We expect to be able to do more and more online, and to do it quicklyfrom ordering food to buying goods, or even finding relationships. If a site feels slow, we'll probably complain to the site owner, our friends and on social media, and possibly not visit the site again, but move on to find alternatives.

Although Internet speeds have increased, websites are getting bigger and more complex by the year, and so they inevitably need to be powered by more powerful technologies to satisfy the impatient users of today. But why is the overall size of websites increasing? Are we getting lazy and taking current, high-speed infrastructures for granted, no longer caring about clean, lean and performant code?

Technology allows us to go bigger, but maybe not necessarily be better when it comes to performance. Servers and Internet connections are getting more sophisticated, and as a result, we feel the need to keep filling them. However, this isn't the time to become lazy. This is the time to utilize the amazing tools that are available for making websites faster, and to learn how to improve user experience and satisfaction. Because nobody likes to wait.

The charts in , sourced from HTTP Archive, show the size and number of HTTP requests of websites, and how both measurements have increased over recent years:

Figure 1. Increase in average website transfer size, 2011-2014

Figure 2. Increase in average number of HTTP requests per website, 2011-2014

From 2010 to 2014, the average total transfer sizebasically the overall weightof a website increased by 150%, compared to the total number of requests (all the assets of the website that need to be loaded), which only increased by around 16%. We can clearly see a trend towards more complex web applications. Our code needs to be performant to handle the rise of sophisticated applications. This book will show you how to make your websites leaner and faster.

Note: An Exercise Routine for Your Website

Throughout this book, you'll notice that I've used various references to exercise routines, notably the Warm Up and Cool Down sections in each chapter. Indeed, the title of this book, Lean Websites , also implies exercise. The primary reasoning behind that idea is that you'll want to make your sites slimmer in order to make them faster. However, additionally, by implementing the techniques discussed in this book over and over, like an exercise routine, you'll develop a web performance muscle memory that will become ingrained in your web development routineestablishing habits that will make building efficient, performant websites seem like second nature.

Who Should Read This Book

This book assumes experience of web development, and familiarity with HTML, CSS, and JavaScript. Some back-end experience would be useful.

Conventions Used

Youll notice that weve used certain typographic and layout styles throughout the book to signify different types of information. Look out for the following items:

Code Samples

Code in this book will be displayed using a fixed-width font, like so: