Hopefully, by now you feel that you have a secure understanding of the work you want to do using D3 to visualize data. We went through some examples and laid some good ground rules for building high-quality data visualizations that not only inform an audience, but also look pretty spectacular in doing so. We also discussed ensuring that your work functions well on mobile.
As much as it pains me, I believe it is nearly time to bid each other adieu. I truly hope you've learned some things and enjoyed the preceding 10 chapters; writing a textbook is a fine balance of getting to the quick and dirty learning bits while also having some fun along the way. Regardless, if you somehow read this thing from beginning to end, my hat's off to you, as we have covered an absolutely mind-boggling array of technologies and approaches to software development.
We started off with some super basic stuff, talking about DOM and CSS. Then, we delved into SVG and learned how to build super pretty web vector graphics, after which we started doing some really neat stuff with D3--remember that chapter on layouts, when we made like a gazillion charts?! We did some cool stuff with Node.js and Canvas, we made a boatload of cool maps; we even put some stuff on Heroku because we're web-development ninjas! Hee-yah! So much stuff!
Lastly, we talked about making truly great stuff with all this technology, and being confident in our work. Whether it's looking to others for inspiration or wiring up a solid test suite to ensure that our work is accurate, data visualization is a craft, one that will only continue to grow in importance as our world becomes ever-more data rich, but one that also requires a degree of precision. Don't worry if you get some things wrong, but do try your best to get everything right.
We are in a truly amazing era of the web where the restrictions that were holding developers back from building brilliant things are slowly being eliminated by smarter approaches, bolder decision making, and better tooling. It is all moving frighteningly fast, but don't let that hold you back from trying new things and playing with code that's on the cutting-edge. There is no other field in computing where you can build things that work so universally, so instantaneously. Although web-development can be really difficult (hello, responsive design!), never has any one set of technologies been so utterly crucial to the way the world consumes information. Having finished this book, you now have, in your possession, a massive warchest of tools that you can try to use. You clearly need to learn a lot more about some of them (particularly the ones I sprinted through, such as Node, Canvas, and TypeScript) to use them effectively, but hopefully I've given you a few things to try out in your journey to understand and make use of all this stuff.
At the very least, you should have everything you need to start visualizing your world with D3 and be able to share it with the world through the magic of the Internet.
Finally, if you get frustrated and need either a hand or somewhere to express your annoyance that this thing you've been working on is still broken two days later, come join us on the D3 Slack channel; there's usually somebody around who's been there and is willing to help.