You may be right that the people who write CoffeeScript already know JavaScript. But as the popularity of CoffeeScript increases so will increase the number of

You may be right that the people who write CoffeeScript already know JavaScript. But as the popularity of CoffeeScript increases so will increase the number of developers who only know CoffeeScript and little to no JavaScript. This may be a temporary problem, though, as it may also become increasingly unnecessary to know JavaScript. But it WILL be a problem. This isn't and won't be limited to CoffeeScript though. There are still a ton of "developers" out there who know jQuery or Dojo or, God forbid, Ext.js but actually know little JavaScript. A friend of mine was recently interviewing a guy who claimed to be a JavaScript developer but didn't know that "foo['bar']" was the same as "foo.bar". No doubt the guy could glue things together in some library blindfolded but the fact remains; he didn't know JavaScript and it cost him a job.