CODEWITHSUNDEEP
javascriptdatedatetimevalidationparsing
Eagles27
Eagles27

Reputation: 45

How to validate whether a string-value is a parsable date-format?

I am running the code below, checking if the string is a date. One of my input values is 'text' which returns the NaN value but my if clause does not work as expected.

function isDate(myDate) {
  console.log('myDate = ' + myDate);
  return Date.parse(new Date(myDate));
}

// var date1 = '1/5/22'; // good date
var date1 = 'test'; // bad date

var whatDate = isDate(date1);

console.log('date = ' + whatDate);

if (whatDate == 'NaN') {
  console.log('bad date');
} else {
  console.log('good date');
}

Upvotes: 2

Views: 1185

Answers (3)

Peter Seliger
Peter Seliger

Reputation: 13376

The following answer, in addition to what already was explained about how to detect a NaN value, wants to reach further.

A check or test function especially if it also carries the prefix is in its name should always return exclusively a boolean value.

  • Thus the OP firstly would implement such a function in a way a user would expect it to work.
  • Secondly the OP had do deal with the NaN issue exactly once within the test function's implementation.

Edit according and thanks to the clarification of RobG

... and ... according to the ECMAScript's spec with instantiating a Date object, the argument passed to the constructor function will be parsed and assigned to the internal thisTimeValue slot. The number type of the latter is the NaN value for a non parsable (invalid) argument.

Any valueOf related operation does return the value of the internal thisTimeValue slot.

Any toString related operation will compute a date string format from the latter value. For a thisTimeValue of NaN the returned string value has to be 'Invalid Date'.

Thus a validation / test implementation could have been something like ...

function isParsableDateRepresentative(...args) {
  return String(new Date(...args)) !== 'Invalid Date';
}

... but preferably it should be closer to the next provided one ...

function isParsableDateRepresentative(...args) {
  return !Number.isNaN(new Date(...args).valueOf());
}

Tests:

function isParsableDateRepresentative(...args) {
  return !Number.isNaN(new Date(...args).valueOf());
}

console.log('new Date("1/5/22") ...', new Date("1/5/22"));
console.log(
  'isParsableDateRepresentative("1/5/22") ...',
  isParsableDateRepresentative("1/5/22")
);
console.log('\nnew Date("test") ...', new Date("test"));
console.log(
  'isParsableDateRepresentative("test") ...',
  isParsableDateRepresentative("test")
);
console.log('\nnew Date(new Date("test")) ...', new Date(new Date("test")));
console.log(
  'isParsableDateRepresentative(new Date("test")) ...',
  isParsableDateRepresentative(new Date("test"))
);

console.log('\nnew Date() ...', new Date());
console.log(
  'isParsableDateRepresentative() ...',
  isParsableDateRepresentative()
);
console.log('\nnew Date(null) ...', new Date(null));
console.log(
  'isParsableDateRepresentative(null) ...',
  isParsableDateRepresentative(null)
);
console.log('\nnew Date(undefined) ...', new Date(undefined));
console.log(
  'isParsableDateRepresentative(undefined) ...',
  isParsableDateRepresentative(undefined)
);
console.log('\nnew Date("") ...', new Date(""));
console.log(
  'isParsableDateRepresentative("") ...',
  isParsableDateRepresentative("")
);
.as-console-wrapper { min-height: 100%!important; top: 0; }

Upvotes: 0

Deniz Karadağ
Deniz Karadağ

Reputation: 761

in your if statement you are checking if whatDate is equal to string "NaN". what you want to check whether whatDate is a number or not.

you can try

if (isNaN(whatDate))

Upvotes: 2

Marco
Marco

Reputation: 7261

You're almost there:

if(whatDate == 'NaN'){
    log.debug('bad date');
}else{
    log.debug('good date');
}

Instead of comparing whatDate to 'NaN' use the function isNaN():

if(isNaN(whatDate)){
    log.debug('bad date');
}else{
    log.debug('good date');
}

Alternatively, if you really want to compare to 'NaN' you first have to convert whatDate to a string:

if((whatDate + "") == 'NaN'){
    log.debug('bad date');
}else{
    log.debug('good date');
}

Is one possibility. Another way would be

if(whatDate.toString() == 'NaN'){
    log.debug('bad date');
}else{
    log.debug('good date');
}

Upvotes: 2

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