How to know string value is an instance of Date in Javascript?

Question

I want to check string value is Date or not ? I use the following code but dose not work:

const date = "2019-12-31T20:30:00+00:00";
if (date instanceof Date) {
    // date is Date....
}

or

if (Object.prototype.toString.call(date) === '[object Date]') {
  // date is Date....
}

Does this answer your question? [Check if a string is a date value](https://stackoverflow.com/questions/7445328/check-if-a-string-is-a-date-value) — mgm793, Jun 13 '20 at 09:51
@gorak `new Date("2020") != "Invalid Date"` but this is also not a valid date string. — swapnesh, Jun 13 '20 at 09:55
@gorak, `new Date("2020") != "Invalid Date" ` I think This condition will always return 'true' since the types 'Date' and 'string' have no overlap — Abolfazl Roshanzamir, Jun 13 '20 at 09:59

score -1 · Answer 1 · answered Jun 13 '20 at 10:01

Your first condition is always true because of you are not converting string to Date. There is two way you can do this.

First, you can construct a Date object with given string and check whether Date is valid or not

const dateString = '2019-12-31T20:30:00+00:00';
const date = new Date(dateString);

if(date.toString() !== "Invalid Date") {
    // String is valid date.
} else {
    // String is not valid date.
}

The other way is, firstly you can check the given string is valid date and then consruct a Date object.

 const dateString = '2019-12-31T20:30:00+00:00';
 const parsed = Date.parse(dateString);

 if(!isNaN(parsed)) {
     // String is valid date.
     const date = new Date(parsed);
 } else {
     // String is not a valid date.
 }

If I change the value of dateString to `"1"` it always returns true while It's not a valid date; — , Jun 13 '20 at 10:06
See [*Why does Date.parse give incorrect results?*](https://stackoverflow.com/questions/2587345/why-does-date-parse-give-incorrect-results) — RobG, Jun 13 '20 at 21:23

How to know string value is an instance of Date in Javascript?

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