en.javascript.info/1-js/02-first-steps/04-variables/2-declare-variables/solution.md

First, the variable for the name of our planet.

That's simple:

let ourPlanetName = "Earth";

Note, we could use a shorter name planet, but it might be not obvious what planet it refers to. It's nice to be more verbose. At least until the variable isNotTooLong.

Second, the name of the current visitor:

let currentUserName = "John";

Again, we could shorten that to userName if we know beyound the reasonable doubt that the user is current.

Modern editors and autocomplete make long variable names easy to write. Don't save on them. Say, a name with 3 words in it is fine.

And if your editor does not have proper autocompletion, get a new one.