JavaScript merge sort

gistfile1.js

function merge(a, b, c) {
    c = c || [];
    if(!a.length && !b.length) return c;

    c.push(a[0] < b[0] || isNaN(b[0]) ? a.shift() : b.shift());
    return merge(a, b, c);
}

function msort(inp) {
    var mid = (inp.length / 2) << 0;
    if(!mid) return inp;
    
    return merge(
        msort(inp.slice(0, mid)),
        msort(inp.slice(mid)));
}

console.log(msort([6,3,5,0,2,4,1,7]));