What does the || operator do?

The || or Logical OR operator finds the first truthy expression in its operands and returns it. This too employs short-circuiting to prevent unnecessary work. It was used before to initialize default parameter values IN functions before ES6 Default function parameters was supported.

console.log(null || 1 || undefined); //logs 1

function logName(name) {
  var n = name || "Mark";
  console.log(n);
}

logName(); //logs "Mark"