Why can i parse invalid date string? [duplicate] - javascript

This question already has answers here:
Why does Date.parse give incorrect results?
(11 answers)
Closed 3 years ago.
I use a function that check if entered value is a valid text for specific purpose in my application.
valid value is a string where it's not valid date or number neither true or false.
checkText(str) {
return isNaN(str) && isNaN(Date.parse(str)) && ['true', 'false'].indexOf(str) == -1;
}
It works properly, but i faced an issue with this string: "New Item 3".
Date.parse("New Item 3") returns a number, but why!!? also, if you changed 3 into any number less than 13 it will return number!
Anyone here can explain to me what happens?

Lesson learned: Date.parse is not a date validator.
Even MDN says:
It is not recommended to use Date.parse as until ES5, parsing of strings was entirely implementation dependent. There are still many differences in how different hosts parse date strings, therefore date strings should be manually parsed (a library can help if many different formats are to be accommodated).
And further down
The ECMAScript specification states: If the String does not conform to the standard format the function may fall back to any implementation–specific heuristics or implementation–specific parsing algorithm. Unrecognizable strings or dates containing illegal element values in ISO formatted strings shall cause Date.parse() to return NaN.
However, invalid values in date strings not recognized as simplified ISO format as defined by ECMA-262 may or may not result in NaN, depending on the browser and values provided

In fact the problem here is coming from Date.parse() method, if you check:
Date.parse("New Item 3");
It will return:
983401200000
console.log(Date.parse("New Item 3"));
So the fact here is that Date.parse() will behave according the browser specifications and may or not return a Number. It depends on the browser.
And you can see from the Date.parse() MDN reference that:
The ECMAScript specification states: If the String does not conform to the standard format the function may fall back to any implementation–specific heuristics or implementation–specific parsing algorithm. Unrecognizable strings or dates containing illegal element values in ISO formatted strings shall cause Date.parse() to return NaN.
However, invalid values in date strings not recognized as simplified
ISO format as defined by ECMA-262 may or may not result in NaN,
depending on the browser and values provided.

Related

Validate if string is a date [duplicate]

This question already has answers here:
Why does Date.parse give incorrect results?
(11 answers)
How to validate a date?
(11 answers)
Closed 2 years ago.
I've seen many articles about this but not quite found what I am looking for yet.
I'm trying to simply check if a string is a date. That string might contains a number such as 2012 though.
var timestamp = Date.parse('foo 2012');
if (isNaN(timestamp) == false) {
var d = new Date(timestamp);
console.log('DATE', d)
}else{
console.log('TEXT');
}
//OUTPUT: DATE Sun Jan 01 2012 00:00:00 GMT+1100 (Australian Eastern Daylight Time)
Why does javascript convert foo 2012 into a date when it's clearly not?
How can I validate that my string is an actual date ?
A string is never a date.
A string can represent a date. There are many ways to represent the same date through different string formats.
This means "validating that a string is a date" is an impossible task. What you can do instead is:
Validate that the format of the string conforms to some well-known format and that its contents are valid.
Try to parse a given string as an expected format and either throw an error or return a "guard" value to indicate that the parsing was not a success.
JavaScript took a third option, which is like option 2, only it returns a value indicating its "best efforts" at working with the garbage input. That's apparently why it saw a year in your string and decided "well, I guess I can make a date with this?" As #Pointy pointed out, it's actually in the spec that if the JavaScript string doesn't match one of the two supported formats, the implementer can decide what the result should be.
I'd highly recommend that if you're dealing with date strings, you should stick with a consistent format. I'm a big fan of ISO 8601 date/time strings because they are time zone aware, easy to sort, and are widely supported (including being easily parsed by JavaScript). If you're requiring the strings are in a standard format, it's easier to do things like finding A RegExp that can validate the input.

new Date() producing valid date from invalid input string [duplicate]

This question already has answers here:
Detecting an "invalid date" Date instance in JavaScript
(52 answers)
Closed 3 years ago.
When I pass "test 2" string in new Date(), I am getting an actual date, how?
I am trying to whether it is a date or not.
console.log(new Date("test 2"));
Passing a string to new Date is the same as using Date.parse.
When a non-standard date string is passed, the result is implementation-dependent; the browser can do whatever it wants, including guessing. On Chrome, your input results in a date, but not on Firefox (NaN is returned).
test isn't part of a date string, so it looks like Chrome just parses the 2:
console.log(new Date('2'));
console.log(new Date('1'));
console.log(new Date('0'));
Essentially, this is undefined behavior, so strange results aren't surprising. Unless the passed string conforms to the format defined in the specification - that is, something like "2011-10-10" or "2011-10-10T14:48:00" or "2011-10-10T14:48:00.000+09:00", the results are unpredictable.
Consider instead figuring out what sort of string format you'd be expecting as an input, and then checking if the format is followed with a regular expression. If so, pass to new Date and see if it gives you a meaningful results; otherwise, don't.
As per MDN:
The ECMAScript specification states: If the String does not conform to the standard format the function may fall back to any implementation–specific heuristics or implementation–specific parsing algorithm.
Google Chrome tries to parse your date and picks up the number as a month. Other browsers may reject the passed value or return something totally different.
Hence please consider the following note:
Parsing of date strings with the Date constructor (and Date.parse(), which works the same way) is strongly discouraged due to browser differences and inconsistencies.
MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date#Parameters
From mdn:
A string representing a simplification of the ISO 8601 calendar date extended format (other formats may be used, but results are implementation-dependent).
You're encountering an implementation-specific attempt to parse your string as a date. It is not recommended to depend on this behaviour.
Because your test text includes a number. See, it's interpreting a number like 1 as January, 2 as February,3 as March, and so on.
new Date( "3")
will give you
Thu Mar 01 2001 00:00:00 GMT+0530 (India Standard Time)
If you use text with no number, e.g. new Date("test") it will throw invalid date.

Why does parsing a locale date string result in an invalid date?

Can someone explain why the following snippets result in an invalid date object?
new Date(new Date().toLocaleString())
// or
Date.parse(new Date().toLocaleString())
This is expressly permitted by the ES5 specification's definition of Date.parse (emphasis mine):
...all of the following expressions should produce the same numeric value in that implementation, if all the properties referenced have their initial values:
x.valueOf()
Date.parse(x.toString())
Date.parse(x.toUTCString())
Date.parse(x.toISOString())
However, the expression
Date.parse(x.toLocaleString())
is not required to produce the same Number value as the preceding three expressions and, in general, the value produced by Date.parse is implementation-dependent when given any String value that does not conform to the Date Time String Format (15.9.1.15) and that could not be produced in that implementation by the toString or toUTCString method.
Since toLocaleString is not required to produce a string conformant to the Date Time String Format YYYY-MM-DDTHH:mm:ss.sssZ, it is allowable for its output not to be parsed correctly by Date.parse.
new Date().toLocaleString() returns the current date in a format new Date() can't parse, resulting in unexpected dates.

How to deserialize JSON text into a date type using Windows 8 JSON.parse?

I'm building a Windows 8 Metro app (aka "Modern UI Style" or "Windows Store app") in HTML5/JavaScript consuming JSON Web Services and I'm bumping into the following issue: in which format should my JSON Web Services serialize dates for the Windows 8 Metro JSON.parse method to deserialize those in a date type?
I tried:
sending dates using the ISO-8601 format, (JSON.parse returns a string),
sending dates such as "/Date(1198908717056)/" as explained here (same result).
I'm starting to doubt that Windows 8's JSON.parse method supports dates as even when parsing the output of its own JSON.stringify method does not return a date type.
Example:
var d = new Date(); // => a new date
var str = JSON.stringify(d); // str is a string => "\"2012-07-10T14:44:00.000Z\""
var date2 = JSON.parse(str); // date2 is a string => "2012-07-10T14:44:00.000Z"
Here's how I got this working in a generic way (though it I'd rather find a format supported out-of-the-box by Windows 8's JSON.parse method):
On the server, I'm serializing my strings using:
date1.ToString("s");
This uses the ISO 8601 date format which is always the same, regardless of the culture used or the format provider supplied (see here for more information).
On the client-side, I specified a "reviver" callback to JSON.parse which looks for dates using a regexp and converts them into a date object automatically.
In the end, the deserialized object will contain actual JavaScript date types and not strings.
Here's a code sample:
var responseResult = JSON.parse(request.responseText, function dateReviver(key, value) {
if (typeof value === 'string') {
var re = /^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2}(?:\.\d*)?)$/
var result = re.exec(value);
if (result) {
return new Date(Date.UTC(+result[1], +result[2] - 1, +result[3], +result[4],+result[5], +result[6]));
}
});
Hope this helps,
Carl
This is not something that's unique to Windows 8's JSON.parse – it's the by-design behavior of the ECMA standard JSON parser. Therefore, there is (and can be) no "out-of-the-box support" for dates.
Per spec, JSON values can only be a String, Number, Boolean, Array, Object, or null. Dates are not supported. (IMO, this is an oversight on the part of the spec, but it's what we have to live with.)
Since there is no date type, your app has to work out how to handle dates on its own. The best way to handle this is to send dates as ISO 8601 strings (yyyy-MM-dd'T'HH:mm:ss'Z') or as milliseconds since the epoch (Jan 1 1970 00:00:00 UTC). The important part here is to make sure time is in UTC.
If performance is important, I would not use a reviver callback with JSON.parse. I did a lot of testing, and the overhead involved with invoking a function for every single property in your object cuts performance in half.
On the other hand, I was honestly surprised with how well testing a regex against every string value stood up against only parsing known property names. Just make sure you define the regex once, outside the loop!
Obviously, the absolute fastest ways to turn JSON values into Dates is if you know exactly what properties need to be parsed for dates. However, given the surprisingly good performance of the regex-based search methods, I don't think it's worth the extra complexity unless you really need the extra performance.
A note on using ISO strings vs milliseconds since epoch: tested independently, milliseconds wins. In IE, there's no difference, but Firefox really seems to struggle with ISO strings. Also note that the Date constructor takes milliseconds in all browsers. It also takes a the ISO string, but not in IE ≤ 8.

How can I parse this date string consistently across browsers?

I'm using Javascript's Date object to parse a string into a milliseconds timestamp. I'm using Date.parse(), and the strings I'm parsing are of the following format: "2012-07-06 12:59:36-0600"
Date.parse performs nicely in Chrome, parsing into the correct timestamp I'd anticipate. However, every other browser returns "NaN" when I run the string through Date.parse().
I know that the Date object implementation is browser-specific, but I'd like to find a javascript solution that's capable of parsing strings of this type for any browser. Any suggestions on what else I could use in Javascript to achieve this?
Convert the input to valid ISO 8601:
Date.parse("2012-07-06 12:59:36-0600".replace(' ', 'T'));
This was tested (and works) in Firefox.
Note:
Note that while time zone specifiers are used during date string
parsing to properly interpret the argument, they do not affect the
value returned, which is always the number of milliseconds between
January 1, 1970 00:00:00 UTC and the point in time represented by the
argument.
https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date/parse
Have you tried DateJS? Maybe you don't want to add another library, but it will solve your crossbrowser problem.
If the format is consistent, you can parse it yourself:
var date = "2012-07-06 12:59:36-0600";
function parseDatetime(input) {
var match = input.match(/(\d{4})-(\d{2})-(\d{2}) (\d{2}):(\d{2}):(\d{2})([-+]\d{4})/);
match.shift(); // discard the "full match" index
match[2]--;
match[4] += parseInt(match[6],10);
return new Date(match[0],match[1],match[2],match[3],match[4],match[5]);
}

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