Join the elements in an javascript array, but let the last separator be different eg: `and` / `or`

formatArrayIntoComma.js

/*
 * Join the elements in an javascript array, 
 * but let the last separator be different eg: `and` / `or`
 * Stackoverflow link: http://stackoverflow.com/questions/15069587/is-there-a-way-to-join-the-elements-in-an-js-array-but-let-the-last-separator-b
 * Credit: Chris Barr - http://stackoverflow.com/users/79677/chris-barr
 */
function formatArray(arr){
    var outStr = "";
    if (arr.length === 1) {
        outStr = arr[0];
    } else if (arr.length === 2) {
        //joins all with "and" but no commas
        //example: "bob and sam"
        outStr = arr.join(' and ');
    } else if (arr.length > 2) {
        //joins all with commas, but last one gets ", and" (oxford comma!)
        //example: "bob, joe, and sam"
        outStr = arr.slice(0, -1).join(', ') + ', and ' + arr.slice(-1);
    }
    return outStr;
}

You could completely omit the outStr variable, and just directly return the result.

… without forgetting to handle the arr.length === 0 case :)