JSON Schema validation library for JavaScript / Node / Express.

npm install schema-validator
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Schema Validation for JavaScript

Barebones schema validation library for things such as database schemas, api data schemas, etc.


$ npm install schema-validator

For browsers, download and include the script validator.js just as you would jquery or another script.


  • Requirement (built-in)
  • Type - uses so make sure you use String, Number, Boolean... etc.
  • Length - By itself it must be this long, otherwise as an object supports the following:
    • Min
    • Max
  • Test (Regular expression tests)
    • Supports an array of RegExps as well.


You create a JSON Schema, where username is a field, and each key:value inside of it is an implementation in validator.

var schema = {
  username: {
    type: String,
    required: true,
    length: {
      min: 3,
      max: 36
    test: /^[a-z0-9]+$/gi

Setup a new Validator against your schema:

var validator = new Validator(schema);

Note there is also debugging support you can enable by adding the following line:

validator.debug = true;

Now we validate against some given information:

var check = validator.check({
  username: "Niji%kokun"

Express Middleware Style:

Schema data will be put on the request object, req.validated, as an Object containing field : data information.

app.get('api/user/add', [ new Validator(schema.user, true) ], function (req, res) {
  res.send(200, req.validated);


app.get('api/user/add', [ (new Validator(schema.user)).middleware ], function (req, res) {
  res.send(200, req.validated);

Creating an extension

Implementing a feature into Validator is easy, you set the field and a callback.

The callback supports a single argument options which contains valuable information.

  • field - The field implementation that is being checked.
  • key - The schema field being checked.
  • data - The data passed from an external source.
  • value - The field implementation data value.
  • error - Sugar method for this.error which was previously used.
    • type - optional argument, it's the error field for the message given. Default is field.
    • message - Error message.
Validator.implement("field", function (options) {
  if ( {
    options.error("Data exists, this is wrong... or right! I don't know!");

  // If you couldn't tell this gives an error back to the validator
  options.error("No check has been done against this key!");

  // and you can set custom field name for the error message object
  options.error("error-field", "This field hasn't been checked yet!");

After your implementation has been ran, the validator will check for errors, if found it will exit out and return the errors. You can pass along multiple errors per run, for an example check the test implementation.


  • Make extensibility easier.
  • Move over to github repository.
  • Make implementations use an object as an argument rather than multiple arguments.
  • Implement nesting feature. Might be useful, I personally can't see one... let me know in issues if you can.
  • Break up implementations into their own folder and make a compiler.

Futuristic / Unfeasible

  • Find a way to show how to do unique without requiring hassle of setup. (JuggleDB?)
    • Essentially you connect in your database and get the collection and check against the key.
    • It's not that hard but there are thousands of databases and ways people do things...


Version 3.2.1

  • Implemented default field.
    • Supported even on required fields, may be subject to change. Let me know in issues how you feel.

Version 3.2

  • Fixed test, now can be run with node
  • Fixed length for Numbers with extended support for Arrays
  • Fixed loop issue where only one value was returned
  • Implemented support for natives no longer need to use strings for types
    • Function, String... are supported, check password.type in test for more information.
  • Implemented debug feature for showing value of fields along with error messages.
  • Simplified roundup.

Version 3.1

  • Extended comments
  • Implemented module exporting for various platforms.

Version 3

  • Remove console logging
  • Implement plugin system - .implement method

Version 2

  • Fix slight bugs in matching validation check
  • Make errors Object based for quick key referencing

Version 1

  • Initial Release.
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