Parsing a date

[blocka]

Very surprised that I could not find anything on this.

If I have a date schema const schema = z.date() and I pass it a date string schema.parse('2022-01-12T00:00:00.000Z')
I would expect to get back a JS Date object. Instead I get an exception that I've passed a string instead of a date.

Am I supposed to use a transform here?

[JacobWeisenburger]

There are a few ways to handle what you are trying to do:

const dateSchema = z.preprocess( arg => typeof arg == 'string' ? new Date( arg ) : undefined, z.date() )
dateSchema.safeParse( '2022-01-12T00:00:00.000Z' ) // success: true
dateSchema.safeParse( new Date( '2022-01-12T00:00:00.000Z' ) ) // success: false

const stringToDate = z.string().transform( arg => new Date( arg ) )
stringToDate.safeParse( '2022-01-12T00:00:00.000Z' ) // success: true
dateSchema.safeParse( new Date( '2022-01-12T00:00:00.000Z' ) ) // success: false

const stringOrDateToDate = z.string().or( z.date() ).transform( arg => new Date( arg ) )
stringOrDateToDate.safeParse( '2022-01-12T00:00:00.000Z' ) // success: true
stringOrDateToDate.safeParse( new Date( '2022-01-12T00:00:00.000Z' ) ) // success: true

Hope this helps. Let me know if you have any questions.

I also added a pull request to add documentation about z.date. Sorry for the confusion cause by not having any documentation.
#881

---

2022-02-11 update:
a dates section has now been added to the README
https://github.com/colinhacks/zod#dates

[Zegnat]

I ran into this today and thought I would add my solution to this discussion in case others come by:

const stringToValidDate = z.string().transform((dateString, ctx) => {
    const date = new Date(dateString);
    if (!z.date().safeParse(date).success) {
        ctx.addIssue({
            code: z.ZodIssueCode.invalid_date,
        })
    }
    return date;
})

I did not want to use preprocess as above, as it seemed to effect the z.input type function. (Or maybe I was just doing it wrong.) And the two transform alternatives given by @JacobWeisenburger could actually lead to invalid dates, meaning even after Zod had parsed the input string it would not be safe to run certain methods.

This transform covers all the cases I need covered. Zod expects a string value in (as I am getting ISO strings from an external API) and will output a Date object only if the string is parsable into a valid date.

[baloodevil]

Is there a way to have stringToValidDate be of type ZodDate (from z.date()) instead of ZodString (from z.string())?

[baloodevil]

Wow! Zod is an incredible library.

Use coerce to do exactly what I was looking for...

const stringToValidDate = z.coerce.date().transform((dateString, ctx) => {
    const date = new Date(dateString);
    if (!z.date().safeParse(date).success) {
        ctx.addIssue({
            code: z.ZodIssueCode.invalid_date,
        })
    }
    return date;
})

[JacobWeisenburger]

Since v3.20, this got way easier.

Let me know if this works for you?

Code updated on 2023-02-25. Thanks to @pilotmoon, for the idea.

const stringToDate = z.string().pipe( z.coerce.date() )
console.log( stringToDate.safeParse( '2023-01-10' ).success ) // true
console.log( stringToDate.safeParse( '2023-13-10' ).success ) // false
console.log( stringToDate.safeParse( null ).success ) // false

---

the dates section has been updated in the README
https://github.com/colinhacks/zod#dates

[pke]

@JacobWeisenburger any idea how to support offsets in coerced date types?
With z.datetime({ offset: true }) is allowed. Any reson why offsets are disabled by default in parsing ISO dates?

[JacobWeisenburger]

@JacobWeisenburger any idea how to support offsets in coerced date types?

Is this what you are looking for?

const stringToDate = z.string().datetime( { offset: true } ).pipe( z.coerce.date() )
console.log( stringToDate.safeParse( '2023-04-05T00:00:00Z' ).success ) // true
console.log( stringToDate.safeParse( '2023-04-05T00:00:00+02:00' ).success ) // true
console.log( stringToDate.safeParse( '2023-04-05T00:00:00.123+02:00' ).success ) // true
console.log( stringToDate.safeParse( '2023-04-05T00:00:00.123+0200' ).success ) // true
console.log( stringToDate.safeParse( '2023-04-05' ).success ) // false
console.log( stringToDate.safeParse( null ).success ) // false

---

Any reson why offsets are disabled by default in parsing ISO dates?

No, idea. Not sure who made that decision.

---

If you found my answer satisfactory, please consider supporting me. Even a small amount is greatly appreciated. Thanks friend! 🙏
https://github.com/sponsors/JacobWeisenburger

[pke]

That new piping interface is worth something ;) Thanks a lot @JacobWeisenburger!

I have to dig deeper into how it works.
So the coerce.data() returns a class whose constructor is fed with the result of the datetime parse?

[McGern]

Hi,

Is there any advice on how to make dates like "2000-04-31" fail? new Date() will return the first day of the next month, so the date will not fail. In the past I have created the date then parsed it into the same format and checked the string values e.g.
"2000-04-31" => May 1st 2000 => formats to "2000-05-01" which is not the same as the original input so can be tested and then fails.

[pilotmoon]

According to the readme as it stands today, you can now do:

const dateValidatorAcceptsString = z.coerce.date();

I don't see any information about pipe() in the docs.

[JacobWeisenburger]

coerce allows the schema to accept any input. I wrote my code the way I did so it only accepts strings as input.

[JacobWeisenburger]

Although, I suppose you could to it this way:

const stringToDate = z.string().pipe( z.coerce.date() )
console.log( stringToDate.safeParse( '2023-01-10' ).success ) // true
console.log( stringToDate.safeParse( '2023-13-10' ).success ) // false
console.log( stringToDate.safeParse( null ).success ) // false

[pcostanz]

@JacobWeisenburger this seems to be a good solution for my usecase of validating that dates are date-like. I'm trying to generate types from Zod objects that make use of this via z.infer<typeof ZObject> where some of the keys use the stringToDate the issue I'm having is that in the inferred types they're coming through as Date types when the value is actually a string that looks like 2024-01-17. Would you expect these to be typed as Date or string after inference? I can obviously handle it by converting those to Dates, but it kind of seems like it might defeat the purpose of the piped coerce. Thanks!

Eg:

const stringToDate = z.string().pipe(z.coerce.date());

export const ZSeason = z.object({
  SeasonId: z.string(),
  Title: z.string(),
  StartDate: stringToDate,
  EndDate: stringToDate,
});

export type TSeason = z.infer<typeof ZSeason>;

// which then produces
type TSeason = {
    SeasonId?: string;
    Title?: string;
    StartDate?: Date;
    EndDate?: Date;
}