Javascript Array unique(k)

Array.prototype.unique = function(k) {
    var self = this;
    var result = [];
    var sublen = 0;
    for (var i = 0, l = self.length; i < l; i++) {
        var v = self[i];
        if (!k) {
            if (result.indexOf(v) === -1) {
                result.push(v);/*from  ww  w.j  a  v  a2 s .co  m*/
            }
            continue;
        }
        if (sublen === 0) {
            result.push(v);
            sublen++;
            continue;
        }
        var is = true;
        for (var j = 0; j < sublen; j++) {
            if (result[j][k] === v[k]) {
                is = false;
                break;
            }
        }
        if (is) {
            result.push(v);
            sublen++;
        }
    }
    return result;
};