js按长度截取字符串，返回按长度分割成的字符串数组

var str = "春节快要放假了，好开心呀！"
var strArr = [];
var n = 3;
for (var i = 0, l = str.length; i < l/n; i++) {
var a = str.slice(ni, n(i+1));
strArr.push(a);
}
console.log(strArr);

结果：["春节快", "要放假", "了，好", "开心呀", "！"]