Echo JS 0.11.0

I totally agree with the general feeling of the article, and I like the suggestion to only allow const / disallow let at the top level 

I find that I often write a function which manipulates, say, an array with push or shift. Then I want to change the algorithm to use concat - oh wait I have to change `const arr = ...` to `let arr = ...`, because that's how concat works. It seems ridiculous