js 数组分组

 
function group(arr, step) {
    return arr.reduce((x, y) => {
        return Array.isArray(x) ? (x[x.length - 1].push(y) == step ? [...x, []] : x) : [[x, y]];
    })
}
group([1, 2, 3, 4, 5, 6, 7, 8, 9, 0],3)

 function group(arr, step) {
            function copyPush(v, item) {
                var res = [];
                for (var i = 0; i < v.length; i++) {
                    res.push(v[i]);
                }
                res.push(item);
                return res;
            }

            return arr.reduce(function(x, y){
                return Array.isArray(x) ? (x[x.length - 1].push(y) == step ? copyPush(x,[]) : x) : [[x, y]];
            })
        }
        //group([1, 2, 3, 4, 5, 6, 7, 8, 9, 0],3)