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Whatever you’re going to make… I find it useful to work in small steps, and test every step you make (using console.log('some useful feedback');) You can log everything, not just Strings, which is really handy.
Make something simple like a form with a text field and a submit button, that appends the user input to some list. That will get you used to user input, form processing in JS, general events and DOM manipulation. Bind to the form submit event and make it prevent default behavior.
Forget about cross-browser issues and just use stuff like querySelector, addEventListener and appendChild. As long as you know those are not cross-browser, worrying about them now will only slow down your progress. Get comfortable with JS first, then worry about them.