For a really good rundown of all the new toys you have with ES2015-17, check out https://babeljs.io/docs/learn-es2015/, a nice guide by the folks at Babel.js, which we will use extensively throughout this book.
Before I go any further, let me clear some confusion about what ES2017 actually is. Initially, the ECMAScript (or ES for short) standards were incremented by cardinal numbers, for instance, ES4, ES5, ES6, and ES7. However, with ES6, they changed this so that a new standard is released every year in order to keep pace with modern development trends, and thus we refer to the year (2017) now. The big release was ES2015, which more or less maps to ES6. ES2016 was ratified in June 2016, and builds on the previous year's standard, while adding a few fixes and two new features. ES2017 is currently in the draft stage, which means proposals for new features are being considered and developed until it is ratified sometime in 2017. As a result of this book being written while these features were in draft, they may not actually make it to ES2017 and thus may need to wait until a later standard to be officially added to the language.