TypeScript - detecting invalid date
In this article, we're going to have a look at how to check if data is invalid in TypeScript.
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:
xxxxxxxxxxconst correctDate = new Date(2022, 10, 15);const 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.
xxxxxxxxxxconst isCorrectDate = (date: Date): boolean => { return date instanceof Date && isFinite(+date); // return date instanceof Date && !isNaN(+date);};// Usage example:const correctDate = new Date(2020, 10, 15);const 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.
xxxxxxxxxxconst isCorrectDate = (date: Date): boolean => { return date instanceof Date && isFinite(date.getTime()); // return date instanceof Date && !isNaN(date.getTime());};// Usage example:const correctDate = new Date(2020, 10, 15);const 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.
xxxxxxxxxxconst isCorrectDate = (date: Date): boolean => { if (date instanceof Date) { const text = Date.prototype.toString.call(date); return text !== 'Invalid Date'; } return false;};// Usage example:const correctDate = new Date(2020, 10, 15);const 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:
xxxxxxxxxxconst isCorrectDate = (date: Date | string): boolean => { 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:const date1 = '2020-10-15';const date2 = '2020-10-x5'; // <-------- incorrect dateconst date3 = 'This is not date'; // <-- incorrect dateconst date4 = new Date(2020, 10, 15);const 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