Merge sort (variant) in JavaScript

mergesort.js

(function(){
    'use strict';

    var randomArray = function(size) {
        var arr = [];
        for(var i=0;i<size;i++) {
            arr.push(Math.round(Math.random() * size * 10));
        }
        return arr;
    };

    var merge = function(a, b) {
        var c = [];
        var l = a.length, m = b.length;
        var i = 0, j = 0;
        while(!(i == l && j == m)) {
            if (i == l) {
                c.push(b[j]);
                j += 1;
            } else if (j == m) {
                c.push(a[i]);
                i += 1;
            } else {
                if (a[i] < b[j]) {
                    c.push(a[i]);
                    i += 1;
                } else {
                    c.push(b[j]);
                    j += 1;
                }
            }
        }
        return c;
    };

    var mergeSort = function(arr, p, r) {
        // console.log('arr: ',arr,' | p: ',p,' | r: ',r);
        if (p < r) {
            var q = Math.floor((p + r) / 2);
            // console.log('Mid:', q);
            var ls = mergeSort(arr, p, q);
            // console.log('ls:', ls);
            var rs = mergeSort(arr, q+1, r);
            // console.log('rs:', rs);
            var merged = merge(ls, rs);
            // console.log(ls,rs,'merged:', merged);
            return merged;
        } else {
            return arr.slice(p, r+1);
        }
    };

    var arr = randomArray(15);
    var now = Date.now();
    var r = mergeSort(arr, 0, arr.length);
    console.log(r);
    console.log(Date.now() - now);
}());

minified.js

function n(n,o){for(c=[],l=n.length,m=o.length,z=x=0;z+x!=m+l;)c.push(z==l?o[x++]:x==m?n[z++]:n[z]<o[x]?n[z++]:o[x++]);return c}function s(l,o,c){var r=~~(o+c)/2;return c>o?n(s(l,o,r),s(l,r+1,c)):l.slice(o,c+1)}

// Usage: s([arr],0,<size>)
console.log(s([81,-7,3,-41,5],0,5))