JavaScript - detecting invalid date
In this article, we're going to have a look at how to check if data is invalid in JavaScript.
Date correctness can be checked basing on internal state of Date object.
Incorrect date object returns:
falsefor callisFinite(myDate),truefor callisNaN(myDate),NaNfrommyDate.getTime()method,- "
Invalid Date" string fortoString()method call.
Quick solution:
xxxxxxxxxxvar correctDate = new Date(2020, 10, 15);var incorrectDate = new Date(NaN);// true - means correct// false - means incorrect//console.log( isFinite( correctDate ) ); // trueconsole.log( !isNaN( correctDate ) ); // trueconsole.log( isFinite( incorrectDate ) ); // falseconsole.log( !isNaN( incorrectDate ) ); // false
Look below to see different practical examples:
This approach is based on fact: isFinite method returns false for incorrect dates.
xxxxxxxxxxfunction isCorrectDate(date) { return date instanceof Date && isFinite(date); // return date instanceof Date && !isNaN(date);}// Usage example:var correctDate = new Date(2020, 10, 15);var incorrectDate = new Date(NaN);console.log( isCorrectDate( correctDate ) ); // trueconsole.log( isCorrectDate( incorrectDate ) ); // falseThis approach is based on fact: incorrect date returns NaN values from getters. So we can make a simple test for example with getTime() method.
xxxxxxxxxxfunction isCorrectDate(date) { return date instanceof Date && isFinite(date.getTime()); // return date instanceof Date && !isNaN(date.getTime());}// Usage example:var correctDate = new Date(2020, 10, 15);var incorrectDate = new Date(NaN);console.log( isCorrectDate( correctDate ) ); // trueconsole.log( isCorrectDate( incorrectDate ) ); // falseThis approach is based on fact: incorrect date object returns "Invalid Date" string for toString() method call. It is good to call to string method with protoype API that prevents methods overriding.
xxxxxxxxxxfunction isCorrectDate(date) { if (date instanceof Date) { var text = Date.prototype.toString.call(date); return text !== 'Invalid Date'; } return false;}// Usage example:var correctDate = new Date(2020, 10, 15);var incorrectDate = new Date(NaN);console.log( isCorrectDate( correctDate ) ); // trueconsole.log( isCorrectDate( incorrectDate ) ); // falseThe example presented in this section allows checking the correctness of the date provided as a string or object. String date should be formatted according to one of the standards:
- IETF-compliant RFC 2822 timestamps,
- ISO 8601.
Run the following code to see the effect:
xxxxxxxxxxfunction isCorrectDate(date) { return isFinite(date instanceof Date ? date : new Date(date)); // return isFinite(date instanceof Date ? date : Date.parse(date)); // return !isNaN(date instanceof Date ? date : new Date(date)); // return !isNaN(date instanceof Date ? date : Date.parse(date));}// Usage example:var date1 = '2020-10-15';var date2 = '2020-10-x5'; // <-------- incorrect datevar date3 = 'This is not date'; // <-- incorrect datevar date4 = new Date(2020, 10, 15);var date5 = new Date(NaN); // <------- incorrect dateconsole.log( isCorrectDate( date1 ) ); // trueconsole.log( isCorrectDate( date2 ) ); // falseconsole.log( isCorrectDate( date3 ) ); // falseconsole.log( isCorrectDate( date4 ) ); // trueconsole.log( isCorrectDate( date5 ) ); // false