直接贴代码吧，最后得到的结果再根据个数进行过滤即可，此处略过。

var a=[['a1','a2'],['b1','b2'],['c1']];
var r = [];
 
for(i=0; i<a.length; i++) {
    len = r.length;
    for(v in a[i]) r.push([a[i][v]]);
    for(j=0; j<len; j++) {
      for(v in a[i]) 
        r.push(r[j].concat(a[i][v]));
    }
}

[["a1"],["a2"],["b1"],["b2"],["a1","b1"],["a1","b2"],["a2","b1"],["a2","b2"],["c1"],["a1","c1"],["a2","c1"],["b1","c1"],["b2","c1"],["a1","b1","c1"],["a1","b2","c1"],["a2","b1","c1"],["a2","b2","c1"]]