ES6的Array.from({length:N})方法创建长度为N的undefined数组，等价于 [...Array(N)]

//创建一个12个undefined组成的数组
Array.from({length:12})
等价于
[...Array(12)]

Array.from({length:12}).forEach((v,i,ar) => {
console.log(v,i)
});

Array.from({length:12}).forEach((v,i,ar) => {
console.log(i+1+'月份');
//console.log('第'+(i+1)+'季度');
//console.log('第'+(i+1)+'学年');
});

[...Array(10)].map((v,i) => 0)//0, 0, 0, 0, 0, 0, 0, 0, 0, 0
[...Array(10)].map((v,i) => i)//0, 1, 2, 3, 4, 5, 6, 7, 8, 9
[...Array(26)].map((v,i) => String.fromCharCode(i + 65))//输出字母表