Rotate the elements in an array in JavaScript

Question

I was wondering what was the most efficient way to rotate a JavaScript array.

I came up with this solution, where a positive n rotates the array to the

Answer 1

When I couldn't find a ready-made snippet to start a list of days with 'today', I did it like this (not quite generic, probably far less refined than the above examples, but did the job):

//returns 7 day names with today first
function startday() {
    const days = ['Sun','Mon','Tue','Wed','Thu','Fri','Sat'];
    let today = new Date();
    let start = today.getDay(); //gets day number
    if (start == 0) { //if Sunday, days are in order
        return days
    }
    else { //if not Sunday, start days with today
        return days.slice(start).concat(days.slice(0,start))
    }
}

Thanks to a little refactor by a better programmer than me it's a line or two shorter than my initial attempt, but any further comments on efficiency are welcome.