joi-extract-type

Provides native type extraction from Joi Schemas for Typescript.

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Joi Schemas are great. But if you use Typescript to define your entities, it is easy to duplicate the definition inside the Schemas and all application interfaces.

This library enhances Joi interfaces to provides an utility to infer the type from a Schema.

Why should you use it

• Avoid duplication from Joi Schemas and application interfaces
• Port javascript applications using Joi to typescript easily
• Does not requires changes to already defined Schemas

Limitation

• Joi is probably a superset of typescript in terms of validation, branching, conditional types, etc. This library is probably suitable for most simples cases, but wont ever prevent every validation error to occur with just static analyses.
• This is experimental and a work in progress. Although I use it in some projects and works for 99% of my schemas.

Installation

npm i --save joi-extract-type

Built for typescript@^3

For typescript 2.9 support checkout branch /typescript@2 or install with:

npm i --save joi-extract-type@ts2-1

Usage

Import the library and patch Joi's typings:

1import * as Joi from '@hapi/joi';
2import 'joi-extract-type';

Create the schemas and use Joi.extractType to infer the type:

1const is_enabled = Joi.boolean();
2type extractBoolean = Joi.extractType<typeof is_enabled>;
3export const extractedBoolean: extractBoolean = true;

Examples

The following code is copied from this library spec, which compiles the code with tsc that should not output any errors.

1const is_enabled = Joi.boolean();
2type extractBoolean = Joi.extractType<typeof is_enabled>;
3export const extractedBoolean: extractBoolean = true;
4
5const full_name = Joi.string();
6type extractString = Joi.extractType<typeof full_name>;
7export const extractedString: extractString = 'string';
8
9const user = Joi.object({ full_name, is_enabled });
10type extractObject = Joi.extractType<typeof user>;
11export const extractedObject: extractObject = {
12  full_name: extractedString,
13  is_enabled: extractedBoolean,
14};
15
16const roles = Joi.array().items(Joi.string());
17type extractArray = Joi.extractType<typeof roles>;
18export const extractedArray: extractArray = ['admin'];
19
20const apply = Joi.array().items(Joi.object({ id: Joi.string() }));
21type extractApply = Joi.extractType<typeof apply>;
22export const extractedApply: extractApply = [{ id: '3' }, { id: '4' }];
23
24const rule = Joi.object({ apply });
25type extractRule = Joi.extractType<typeof rule>;
26export const extractedRule: extractRule = { apply: extractedApply };
27
28export const jobOperatorRoleSchema = Joi.object({
29  id: Joi.string().required(),
30  user_id: Joi.string().required(),
31  job_id: Joi.string().required(),
32  role: Joi.string().valid(['recruiter', 'requester']),
33  pipeline_rules: Joi.array().items(rule),
34});
35type extractComplexType = Joi.extractType<typeof jobOperatorRoleSchema>;
36export const extractedComplexType: extractComplexType = {
37  id: '2015',
38  user_id: '102',
39  job_id: '52',
40  role: 'admin',
41  pipeline_rules: [extractedRule],
42};
43
44// typeof extractedComplexType
45// const extractedComplexType: Joi.extractMap<{
46//     id: Joi.StringSchema;
47//     user_id: Joi.StringSchema;
48//     job_id: Joi.StringSchema;
49//     role: Joi.StringSchema;
50//     pipeline_rules: Joi.ArraySchema<Joi.extractMap<{
51//         apply: Joi.ArraySchema<Joi.extractMap<{
52//             id: Joi.StringSchema;
53//         }>>;
54//     }>>;
55// }>