javascript怎么把一个元素列表中的以4个元素为一个单位，

Array.prototype.chunk = function (len) {
    var len = parseInt(len);
    if (len <= 1 || this.length < len)
        return this;
    var groups = [], loop = Math.ceil(this.length / len);
    for (var i = 0; i < loop; i++)
        groups.push(this.slice(len * i, len * (i + 1)));
    return groups;
}
var arr=[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16];
arr=arr.chunk(4); // [[1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,16]]