What does a `+` in front of a Date do?

Question

I found some code from a departed colleague and no one is sure what the plus in front of the following Date objects is doing.

return {
  isActive: +new Date(notice.reportedAt) === +this.activeNoticeReportedAt,
  ...
}

I feel like it is some kind of JavaScript trick that is supposed to protect against undefined, but that is just a wild guess.

Please not that activeNoticeReportedAt is already a Date

https://stackoverflow.com/questions/221539/what-does-the-plus-sign-do-in-new-date — Adam, Nov 20 '18 at 15:16

score 4 · Accepted Answer · answered Nov 20 '18 at 15:14

It turns it into a number, which represents the date's Unix timestamp in milliseconds:

> +new Date()
< 1542726854220

The reason for using it here is that Date objects can't be compared using the == operator, because that only checks for object equality, not value equality:

> x = new Date("2017-01-01")
> y = new Date("2017-01-01")
> x == y
false

What does a `+` in front of a Date do?

1 Answers1