排列组合

 1     var data = [‘a‘, ‘b‘, ‘c‘, ‘d‘];
 2     function getGroup(data, index = 0, group = []) {
 3         var newArr = [];
 4         newArr.push(data[index]);
 5         for (var i = 0; i < group.length; i++) {
 6             newArr.push(group[i] + ‘,‘ + data[index]);
 7         }
 8         group.push(...newArr);
 9         //  group.push.apply(group, newArr);
10         if (index + 1 >= data.length) return group;
11         else return getGroup(data, index + 1, group);
12     }
13     console.log(getGroup(data));