Original quote is "Any application that can be written in Javascript will eventually be written in Javascript."
It is a quote from Jeffery Atwood, the co-founder of stackoverflow. blog.codinghorror.com/the-principle-of-least-power
Which in turn is based on the rule of least power, which says it is better to use the least powerful tool for the job.
Basically Javascript (at the time 2007, it's probably not most powerful language), and also because of its continue rise in popularity and ubiquitous, there is momentum to write more and more stuff in Javascript.
As he predicted, Javascript what used to be a Front End thing only, with Node.js in 2009, it become gradually become used for backend widely. Now become used more and more for things it was never original designed for.
Yes, you can write a compiler/interpreter for Javascript in Javascript. There is nothing wrong with that.