koa-joi-validator-middleware

Koa 2 middleware for validating Joi schemas

TLDR

Problem:

• Have a Koa 2 web server
• Want to validate with Joi

Solution:

const Koa = require('koa');
const Joi = require('joi');
class koaJoiValidator = require('koa-joi-validator-middleware');

const schema = Joi.object({...});
const config = {...};

const app = new Koa();
app.use(koaJoiValidator(schema, config));

app.use(async ctx => {
  // Here you can be sure that the specified validation passed
});

Examples

1. Basic usage

By default, only the schema parameter is needed. In this case the middleware will validate the ctx.request.body object and throws an Error with a default message if it fails.

...
const schema = Joi.object({...});

const app = new Koa();
app.use(koaJoiValidator(schema));
...

2. Custom onError string parameter

You can specify an onError key in the second, config parameter. If this is a string it overwrites the default error message thrown.

...
const schema = Joi.object({...});
const config = {
  onError: 'Hey You, send me a proper request!'
};

const app = new Koa();
app.use(koaJoiValidator(schema, config));
...

3. Custom onError function parameter

The onError parameter can be a function as well which is called when the validation fails with the following parameters: ctx, next, error. Here ctx and next are the standard Koa middleware parameters and error is the ValidationError returned by Joi.

...
const schema = Joi.object({...});
const config = {
  onError: ctx => ctx.render('errorPage')
};

const app = new Koa();
app.use(koaJoiValidator(schema, config));
...

4. Custom getSubject function parameter

By default, the middleware validates the ctx.request.body object but this can be overwritten with the getSubject function. It takes ctx as the input parameter and is expected to return the object that should be validated.

...
const schema = Joi.object({...});
const config = {
  getSubject: ctx => ctx.session
};

const app = new Koa();
app.use(koaJoiValidator(schema, config));
...

API

Parameter	Optional	Type
schema	no	Joi schema
config	yes	Object
config.onError	yes	String or Function(ctx, next, error)
config.getSubject	yes	Function(ctx)

Note: This middleware does not contain Joi as an inner dependency, only as peer dependency. This means it can be updated individually when a new version comes out but it also means you need to install it separately.