为什么我的数组会被覆盖？

Question

我正在使用node.js进行项目,我正在尝试将某些日期添加到数组中.但是,当我这样做时,它会覆盖整个数组,并添加当前日期.来源如下:

let startDate = new Date(2014, 0, 8, 19, 0, 0)
let endDate = new Date(2014, 0, 11, 19, 0, 0)
let datesToDownload = []
let datesInDB = [new Date(2014, 0, 8, 19, 0, 0), new Date(2014, 0, 9, 19, 0, 0), new Date(2014, 0, 10, 19, 0, 0), new Date(2014, 0, 8, 11, 0, 0)]

for (let i = startDate; i <= endDate; i.setDate(i.getDate() + 1)) {
  console.log('CHECKING DATE: ' + i.toDateString())

  if (!(datesInDB2.indexOf(i.toDateString()) >= 0)) {
    console.log('NEW RECORD FOUND FOR: ' + i.toDateString())
    datesToDownload.push(i)
    console.log('i: ' + i)

    for (let j in datesToDownload) {
      console.log('element ' + j + ': ' + datesToDownload[j])
    }
  }
}

输出看起来像这样:

CHECKING DATE: Wed Jan 08 2014
NEW RECORD FOUND FOR: Wed Jan 03 2014

i: Wed Jan 08 2016 20:00:00 GMT-0400 (Eastern Daylight Time)
element 0: Wed Jan 08 2016 20:00:00 GMT-0400 (Eastern Daylight Time)

CHECKING DATE: Thur Jan 09 2016
NEW RECORD FOUND FOR: Thur Jan 09 2016

i: Thur Jan 09 2016 20:00:00 GMT-0400 (Eastern Daylight Time)
element 0: Thur Jan 09 2016 20:00:00 GMT-0400 (Eastern Daylight Time)
element 1: Thur Jan 09 2016 20:00:00 GMT-0400 (Eastern Daylight Time)

CHECKING DATE: Fri Jan 10 2016
NEW RECORD FOUND FOR: Fri Jan 10 2016

i: Fri Jan 10 2016 20:00:00 GMT-0400 (Eastern Daylight Time)
element 0: Fri Jan 10 2016 20:00:00 GMT-0400 (Eastern Daylight Time)
element 1: Fri Jan 10 2016 20:00:00 GMT-0400 (Eastern Daylight Time)
element 2: Fri Jan 10 2016 20:00:00 GMT-0400 (Eastern Daylight Time)

......

请注意,虽然正在添加元素,但元素是如何更改为当前插入的日期.

为什么会这样？我该怎样预防呢？

Answer 1

您在每次迭代时将完全相同的Date实例推送到数组中.但是,您可以创建它的副本:

  datesToDownload.push(new Date(i));