两个有序数组合并为一个有序数组

function merge(arr1, arr2){
    var arr = [];
    if (arr1.length === 0) {
        return arr = arr2;
    }
    if (arr2.length === 0) {
        return arr = arr1;
    }
    var i = 0;
    var j = 0;
    for (var m = 0; m < arr1.length; m++) {
        for (var n = j; n < arr2.length; n++) {
            if (arr1[m] < arr2[n]>) {
                arr.push(arr1[m]);
                i++;
            } else {
                arr.push(arr2[n]);
                m--;
                j++;
                break;
            }
        }
    }

    if (i < arr1.length) {
        return arr = arr.concat(arr1.slice(i, arr1.length));
    }
    if (j < arr2.length) {
        return arr = arr.concat(arr2.slice(j, arr2.length));
    }
}