express-jsonschema

1.1.6 verified Sat Apr 25 auth: no javascript maintenance

Express middleware for JSON Schema validation, currently at version 1.1.6. It leverages the jsonschema library to validate request bodies against JSON Schema v4. The library provides a simple validate() middleware that attaches validation results to req.validations. Error handling is left to the developer, allowing custom responses. Compared to express-validator or Joi, this library decouples validation logic from schema definitions. It is in maintenance mode, with the last release in 2016 and no recent updates.

Common errors

error TypeError: validate is not a function ↓

cause Attempted to use default import without destructuring.

fix

Use const { validate } = require('express-jsonschema');

error Cannot read property 'body' of undefined ↓

cause The validate() call is missing the request property key, e.g., validate({ body: schema }).

fix

Pass an object with key 'body', 'query', or 'params'.

Warnings

gotcha The validate() function expects an object with keys 'body', 'query', or 'params' - not just a schema object. ↓

fix Use validate({ body: schema }) instead of validate(schema).

gotcha Error handling must be explicitly implemented; unhandled validation errors will crash the app. ↓

fix Add Express error middleware checking for err.name === 'JsonSchemaValidation'.

deprecated The project has not been updated since 2016 and does not support modern Express versions (4.17+). ↓

fix Consider migrating to @express-validator/express-validator or joi-based middleware.

Install

npm install express-jsonschema

yarn add express-jsonschema

pnpm add express-jsonschema

Imports

validate

wrong

const validate = require('express-jsonschema');

correct

const validate = require('express-jsonschema').validate;

The default export is an object; validate is a named export. CommonJS only.

JsonSchemaValidation

wrong

const { JsonSchemaValidation } = require('express-jsonschema');

correct

const JsonSchemaValidation = require('express-jsonschema').JsonSchemaValidation;

JsonSchemaValidation is a class used for error handling; it is not a default export.

validate (ESM)

wrong

import validate from 'express-jsonschema';

correct

import { validate } from 'express-jsonschema';

ESM imports are supported but not documented; use named import.

Quickstart

Demonstrates setting up an Express endpoint with JSON Schema validation for the request body and a custom error handler.

const express = require('express');
const { validate } = require('express-jsonschema');
const app = express();
app.use(require('body-parser').json());

const schema = {
  type: 'object',
  properties: {
    name: { type: 'string' },
    age: { type: 'number' }
  },
  required: ['name']
};

app.post('/user', validate({ body: schema }), (req, res) => {
  res.json({ valid: true });
});

app.use((err, req, res, next) => {
  if (err.name === 'JsonSchemaValidation') {
    res.status(400).json({ errors: err.validations });
  } else {
    next(err);
  }
});

app.listen(3000);