Unique array combination generation

gistfile1.js

Compare.prototype.getCombinations = function(arr) {
    var r = 2;
    var pool = arr;
    var n = pool.length;
    if(r > n) {
        return;
    }
    var indices = [0,1];
    var res = [];
    var tmp = [];
    for(var i = 0;i < indices.length;i++) {
        tmp.push(pool[indices[i]]);
    }
    res.push(tmp);

    (function() {
        while(true) {
            var reversed_ind = [1,0];
            var i;
            for(i = 0;i<reversed_ind.length;i++) {
                if(indices[reversed_ind[i]] != (reversed_ind[i] + n - r))
                    break;
                if(i==reversed_ind.length-1) {
                    return res;
                }
            }
            
            indices[reversed_ind[i]] += 1;
            var tmp = [0,1].slice(reversed_ind[i]+1,r);
            for(var j = 0;j<tmp.length;j++) {
                indices[tmp[j]] = indices[tmp[j]-1] + 1;
            }
            
            var tmp = [];
            for(var x = 0; x < indices.length;x++) {
                tmp.push(pool[indices[x]]);
            }
            res.push(tmp);
        }
    })();
    return res;
};