[英]Why is my array being overwritten?
我正在為項目使用node.js,並且試圖將某些日期添加到數組中。 但是,當我這樣做時,它將覆蓋添加當前日期的整個數組。 資料來源:
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])
}
}
}
輸出看起來像這樣:
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)
......
請注意,盡管添加了元素,但元素如何全部更改為當前插入日期。
為什么會這樣呢? 我該如何預防?
您每次迭代都將完全相同的Date實例推入數組。 但是,您可以創建它的副本 :
datesToDownload.push(new Date(i));
日期是一個對象,並通過引用傳遞。 在for循環中,您正在更改日期:
for (let i = startDate; i <= endDate; i.setDate(i.getDate() + 1)) {
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