It's an opinionated book that sets out a subset of JavaScript that you should use, avoiding all the 'bad parts'. This subset is what tools like JSLint and JSHint were designed to promote - they flag you up if you use a bad part. It's a seminal work. These days I find some of its rules a little dogmatic (for instance I like the 'new' keyword now), but I'm glad I went through a phase of sticking to it relgiously for a while. It taught me to stop bitching about the weird parts, just avoid them instead. And when you do this, you end up loving the language and making cool shit with it. Which is a good situation to be in, because it's the most widely distributed runtime in the world.