头条面试官：用迭代器实现打印某一年的日历

当时是懵逼的，后面上网查也查不到。

只能认真看ES6文档。

直接上代码吧。

class RangeIterator {
  constructor(year) {
    this.count = 0
    this.year = year
    this.fullDays = year % 4 === 0 ? 366 : 365
    this.firstDay = new Date(`${year}-01-01 00:00:00`)
  }

  [Symbol.iterator]() {
    return this
  }

  next() {
    if (this.count <= this.fullDays) {
      let now = new Date(this.firstDay)
      now.setDate(this.count)
      this.count ++
      return {
        value: `${now.getMonth() + 1}.${now.getDate()}`,
        done: false
      }
    }
    return {
      value: undefined,
      done: true
    }
  }
}

function range (year) {
  return new RangeIterator(year)
}

for (let iter of range(2020)) {
  console.log(iter)
}