Discussion on: How would you refactor this JS function?

Leaving out all further context, this might be one of the rare occasions where to make use !! (double ! operator)

const lineChecker = (line = '', isFirstLine = false) => {
  if (!!line) {
    return isFirstLine ? `<h1>${line}</h1>` : `<p>${line}</p>`;
  }
  return '<br/>';
};

Note: After looking through some other solutions, I figured using !! introduces (or solves? I wouldn't know) a problem when passing unexpected falsy - values such as null, false or undefined.

I'd still say it's a pretty good example for refactoring. Even though it seems fairly easy to overengineer if you adhere to the 'functions do a single thing' mantra.