It's called a spread operator, you can use it to define "the rest" of arguments, like (a, b, ...rest) and that'll be an array of the additional arguments. You can call this as myFunc(a, b, c, d) and the rest argument will contain [c, d]. I hope this makes sense. :)

Could you explain what is doing ...names?

Nice one!

Perfect!

This solution uses a OR operator to evaluate whether the property (string or number) exists in the object ({string: "Zach", number: "Monica"}). If it does it returns the property value. If it doesn't, it returns 'the dog'. Does it make sense?