Whilst it's probably impossible to write code without understanding anything about scope, you can actually get quite far without understanding lexical scope and closures.

For example, I've worked on a load of JS projects where every function is first-order, named and written at the top level, except for a few clearly redundant anonymous callbacks like `function(x) { return foo(x); }`. Obviously that code has been written without understanding first-class functions, lexical scope, closures, etc. but it worked.

I've also been in the reverse situation in code reviews: where I've made some use of lexical scope in my code, and had to explain what lexical scope and closures are to the other members of the team.