Extending Joi with Typescript: Preserving types

[digitalcortex]

Support plan

• Community
• Is it stopping my project? yes
• Is it affecting my production? no

Context

• node version: 13.12.0
• module version: 17.1.1
• environment (e.g. node, browser, native): node
• used with (e.g. hapi application, another framework, standalone, ...): feathersjs

How can we help?

I'm trying to write multiple custom extensions for Joi using Typescript. The problem is, Joi.extend() seems to be returning "any" type which totally breaks autocomplete. I tried arranging my extension in the following way:

`import mongoose from 'mongoose'
import Joi from '@hapi/joi';

export function ExtendJoiWithObjectId(root: T) {

interface ExtendedStringSchema {
    objectId(): ExtendedStringSchema;
}

interface ObjectIdJoi {
    string(): ExtendedStringSchema;
}

return root.extend((joi) => {
    return {
        type: 'objectId',
        base: joi.string(),
        messages: {
            'objectId.valid': '"{{#label}}" must be a valid mongo id'
        },
        coerce(value, helpers) {
            return { value };
        },
        validate(value, helpers) {
            if (!mongoose.isValidObjectId(value)) {
                return helpers.error('objectId.valid');
            }
        }
    };
}) as ObjectIdJoi; 

}`

but it makes extensions impossible to combine with each other. Is there any good pattern that would allow me to extend Joi and combine all extensions in a single type definition?

[SimonSchick]

import * as Joi from '@hapi/joi';

interface ObjectIdJoi extends Joi {
    string(): ExtendedStringSchema;
}

joi.extend also takes a vararg.

[abhisekp]

interface ObjectIdJoi extends BaseJoi.StringSchema {
  objectId(): this;
}

Ref: http://definitelytyped.org/docs/joi--joi/modules/joi.html#string

[ignacioambia]

Hi! @hueniverse at the end of the day, how did you solve it?