如何 将一个字符串分割成指定位数的数组，并使用他?

var str="123456789"
var data = str.split("")
var result = [];
for(var i=0;i<data.length;i+=3){
    result.push(data.slice(i,i+3));
}
console.log(result)                //[Array(3), Array(3), Array(3)]
console.log(result[0])             //['1', '2', '3']
console.log(result[0][0])          //1