How to check for dayjs type with zod?

[anthonyma94]

I'm using Day.js extensively in my application. The way to check for dayjs type is to check instanceof dayjs (the function):

import dayjs from "dayjs";
const date = dayjs();
console.log(date instanceof dayjs) // true

The param type of z.instanceof only accepts classes with constructors, but it works in runtime for checking instanceof dayjs. This means that I have to typecast dayjs as any every time I need it in instanceof:

const dateType = z.instanceof(dayjs as any);

z.infer also infers this as any, which doesn't really help me.

How can I infer dayjs properly?

[dvakatsiienko]

The solution didn't worked for me causing an error.

Cannot read properties of undefined (reading 'name')
TypeError: Cannot read properties of undefined (reading 'name') at Object.instanceOfType [as instanceof] (webpack-internal:///./node_modules/zod/lib/index.mjs:3065:43)

But this works:

import dayjs, { type Dayjs } from 'dayjs';

...

z.instanceof(dayjs as unknown as typeof Dayjs)

[jhigdon]

thank you, I needed this as well, though I am unsure why :)

[aki-caffeine]

This answer is very helpful to me. However, I don't know why this coding works properly.

Is there anyone who can explain?

[almogzur]

Thank You

[infodusha]

If anyone want to haver a proper version with no type-cast:

const zodDay = z.custom<Dayjs>((val) => val instanceof dayjs, 'Invalid date');

[Zain-Bin-Arshad]

Or you can use isDayjs like this:

const zodDay = z.custom<Dayjs>((val) => dayjs.isDayjs(val), "Invalid date");