How do I convert strings into dates in Javascript? [duplicate]

Question

I have a list of string dates that I retrieve from a website.

const appDate = await page.evaluate(() => {
  const dates = Array.from(document.querySelectorAll('li.det-comment-list-every div.comment-date'))
  return dates.map(font => font.textContent) 
});

I tried to convert them into Date objects in a for loop.

Example of appDate array :

['2018/8/22 13:52', '2018/5/11 22:36', '2018/7/20 07:13', '2018/5/30 04:04', '2018/3/26 18:21', '2019/3/20 17:46', '2019/3/18 13:01', '2019/3/18 07:27', '2019/3/17 23:10', '2019/3/17 20:39' ]

let nDates = [];
for(let date of appDate){
  var d = new Date(date);
  nDates.push(d);
}
console.log(nDates);

However, the console gives me "invalid date".

[ Invalid Date, Invalid Date, Invalid Date, Invalid Date, Invalid Date, Invalid Date, Invalid Date, Invalid Date, Invalid Date, Invalid Date ]

How can I get my dates to convert into date format?

Answer 1

You might have confused that for..of with for..in, vice versa. You have to be careful with iterating arrays using for..in, it iterates through enumerable properties of an object as well. Try doing this instead:

const dates = ['2018/8/22 13:52', '2018/5/11 22:36', '2018/7/20 07:13', '2018/5/30 04:04', '2018/3/26 18:21', '2019/3/20 17:46', '2019/3/18 13:01', '2019/3/18 07:27', '2019/3/17 23:10', '2019/3/17 20:39' ]
        
const nDates = [];
for(let date of dates){
  const d = new Date(date);
  nDates.push(d);
}
console.log(nDates);

If you insist on using a for..in loop, you will need to iterate via its key-value pairs:

const nDates = [];
for(let index in dates){
  const d = new Date(dates[index]);
  nDates.push(d);
}
console.log(nDates);

Or better still, a shorter, one-liner approach:

const nDates = dates.map(date => new Date(date));

console.log(nDates);

Answer 2

This is a case of wrong use of for..in.. loop. If you try to log your date in for in loop, you'll see that date is actually the index of the element.

var appDate = ['2018/8/22 13:52', '2018/5/11 22:36', '2018/7/20 07:13', '2018/5/30 04:04', '2018/3/26 18:21', '2019/3/20 17:46', '2019/3/18 13:01', '2019/3/18 07:27', '2019/3/17 23:10', '2019/3/17 20:39' ]

let nDates = [];

for(let date in appDate){
   console.log(date);  // 0 1 2 3 4 5 6 7 8 9
   var d = new Date(date);
   nDates.push(d);
}

You can use for..of or any other for loop or map to get the converted dates.

Now that you've updated the question, please verify that the dates array contains valid dates by logging them in the loop.