express-json-validator-middleware

express.js middleware for validating requests against JSON Schema

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Looking for contributors!

I can no longer dedicate as much of my time to maintaining this library, this is an open call for contributors. Please shoot me an email at vacekj at outlook.com if you would like to contribute or take over the project.

Coming from express-jsonschema? Read our migration notes

Major version 1.x of this module uses ajv@5, read their changelog and migration guide here.

Major version 2.x uses ajv@6 in order to support draft-07 of JSON Schema. Please keep in mind that you have to manually configure ajv to support draft-06 schema files from now on (see https://github.com/epoberezkin/ajv#using-version-6).

Why use this library over express-jsonschema ?

• Performance - ajv offers a significant performance boost over JSONSchema.
• Latest JSON Schema Standard - ajv supports JSON Schema v7 proposal.
• Active Maintenance - express-json-validator-middleware is being actively maintained.

Why validate with JSON schemas?

• Simple - JSON schemas are a simple and expressive way to describe a data structure.
• Standard - JSON schemas are not specific to Javascript. In fact, they are used just about everywhere.
• Fail-Fast - Catch errors early in your logic, evading confusing errors later.
• Separate Validation - Keep your routes clean. Validation logic doesn't need to be defined in your route handlers.
• Error Messaging - Ajv provides you with rich error objects that can easily be transformed into human-readable format.
• Documentation - Creating a JSON Schema is another way of documenting your application.

Installation

$ npm install express-json-validator-middleware

--save is no longer necessary as of npm@5

Getting started

1. Require the module

var { Validator, ValidationError } = require('express-json-validator-middleware');

2. Initialize a Validator instance, optionally passing in an ajv#options object

var validator = new Validator({allErrors: true});

3. Optional - Define a bound shortcut function that can be used instead of Validator.validate

var validate = validator.validate;

4. Use the Validator.validate method as an Express middleware, passing in an options object of the following format:

Validator.validate({
    requestProperty: schemaToUse
})

Example: Validate req.body against bodySchema

app.post('/street/', validate({body: bodySchema}), function(req, res) {
    // route code
});

Error handling

On encountering erroneous data, the validator will call next() with a ValidationError object. It is recommended to setup a general error handler for your app where you will catch ValidationError errors

Example - error thrown for the body request property

ValidationError {
    name: 'JsonSchemaValidationError',
    validationErrors: {
        body: [AjvError]
    }
}

More information on ajv#errors

Example Express app

var express = require('express');
var bodyParser = require('body-parser');

var { Validator, ValidationError } = require('express-json-validator-middleware');


// Initialize a Validator instance first
var validator = new Validator({allErrors: true}); // pass in options to the Ajv instance

// Define a shortcut function
var validate = validator.validate;

// Define a JSON Schema
var StreetSchema = {
    type: 'object',
    required: ['number', 'name', 'type'],
    properties: {
        number: {
            type: 'number'
        },
        name: {
            type: 'string'
        },
        type: {
            type: 'string',
            enum: ['Street', 'Avenue', 'Boulevard']
        }
    }
}


var app = express();

app.use(bodyParser.json());

// This route validates req.body against the StreetSchema
app.post('/street/', validate({body: StreetSchema}), function(req, res) {
    // At this point req.body has been validated and you can
    // begin to execute your application code
    res.send('valid');
});

// Error handler for validation errors
app.use(function(err, req, res, next) {
    if (err instanceof ValidationError) {
        // At this point you can execute your error handling code
        res.status(400).send('invalid');
        next();
    }
    else next(err); // pass error on if not a validation error
});

Validating multiple request properties

Sometimes your route may depend on the body and query both having a specific format. In this example we use body and query but you can choose to validate any request properties you like.

var TokenSchema = {
    type: 'object', // req.query is of type object
    required: ['token'], // req.query.token is required
    properties: {
        uuid: { // validate token
            type: 'string', 
            format: 'uuid',
            minLength: 36,
            maxLength: 36
        }
    }
}

app.post('/street/', Validator.validate({body: StreetSchema, query: TokenSchema}), function(req, res) {
    // application code
});

A valid request must now include a token URL query. Example valid URL: /street/?uuid=af3996d0-0e8b-4165-ae97-fdc0823be417

Using dynamic schema

Instead of passing in a schema object you can also pass in a function that will return a schema. It is useful if you need to generate or alter the schema based on the request object.

Example: loading schema from the database

// Middleware executed before validate function

function loadSchema(req, res, next) {
    getSchemaFromDB()
        .then((schema) => {
            req.schema = schema;
            next();
        })
        .catch(next);
}

// function that returns a schema object
function getSchema(req) {
	// return the schema from the previous middleware or the default schema
    return req.schema || DefaultSchema;
}

app.post('/street/', loadSchema, Validator.validate({body: getSchema}), function(req, res) {
    // route code
});

Custom keywords

Ajv custom keywords must be defined before any validate() middleware

Example:

var { Validator, ValidationError } = require('express-json-validator-middleware');
var validator = new Validator({allErrors: true});

validator.ajv.addKeyword('constant', { validate: function (schema, data) {
  return typeof schema == 'object' && schema !== null
          ? deepEqual(schema, data)
          : schema === data;
}, errors: false });

// route handlers with validate()

More info on custom keywords: ajv#customs-keywords

Ajv instance

The Ajv instance can be accessed via validator.ajv.

var { Validator, ValidationError } = require('express-json-validator-middleware');
var validator = new Validator({allErrors: true});

validator.ajv // ajv instance

Tests

Tests are written using Mocha & Chai

npm install
npm test

More documentation on JSON schemas

• spacetelescope's understanding json schema

Migrating from express-jsonschema

In express-jsonschema, you could define a required property in two ways. Ajv only supports one way of doing this.

// CORRECT
{
    type: 'object',
    properties: {
        foo: {
            type: 'string'
        }
    },
    required: ['foo'] // <-- correct way
}

// WRONG
{
    type: 'object',
    properties: {
        foo: {
            type: 'string',
            required: true // nono way
        }
    }
}

Credits

• Maintained by @JouzaLoL
• Original Module by @trainiac
• PRs: see Contributors