[Vuejs]-I have a route component, why are my props not automatically updating when I set them in the route definition?

Router do not pass id to props.In your case you can find id in this.$route.params

Even if you use something like /book/:id in router itself, that id param will live in this.$route.params.id.

So you need something like :

 created() {
  this.getBook(this.$router.params.id);
 },

And btw, in watcher too.