[Solved] Arrays to objects

Some diversity of approaches (admittedly esoteric, but fun!):

function firstAndLast(a, o){
    return !(o = {}, o[a.shift()] = a.pop()) || o;
}

console.log(firstAndLast([1,2,3,4,5]));
console.log(firstAndLast(['a','to','z']));

https://jsfiddle.net/brtsbLp1/

And, of course:

function firstAndLast(a, o){
    return !(o = o || {}, o[a.shift()] = a.pop()) || o;
}

console.log(firstAndLast(['a','to','z']));
console.log(firstAndLast(['a','to','z'], {a:'nother',obj:'ect'}));

https://jsfiddle.net/brtsbLp1/1/

Another fun one:

function firstAndLast(a){
    return JSON.parse('{"'+a.shift()+'":"'+a.pop()+'"}');
}

https://jsfiddle.net/brtsbLp1/2/

That last one will choke on the first being a number (since labels aren’t allowed to be numbers only), plus other issues in general. But this should give some food for thought. The other answers are a bit more obvious.