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A library to validate a data structure and create fake content at the same time. Works great with React.js.

React Prop Schema

A library to validate a data structure and create fake content at the same time. Works great with React.js and can be used to replace React.PropTypes.

Build Status

Installation / Usage

This has been created to be used as a CommonJS module, using node, browserify or something similar. If you need a good starting point for using browserify, have a look at this project's

Even though this library is written in CoffeeScript, a JS version can be created using npm run precompile. Versions uploaded to npm will contain the JS files in dist.

Basically, you just need to run

$ npm install --save react-prop-schema

and then you should be able to require('react-prop-schema') in your code.

Use in Production

If you use browserify, you should compile your code with envify and uglifyify for production (so you can get rid of dead code).

Please note that if you set NODE_ENV=production, this:

  • prevents loading and embedding faker.js, saving you about 140kB of bandwidth
  • mutes all validation warnings (but does not remove validation code)

What's so cool about this?

Let's say you have a data structure, represented by the following JSON:

  "name": "Pascal",
  "level": 42

Everything is fine, but you are a skeptic, so you want to validate this data. Let's assume you have a tool that can validate this data using the following schema description:

  "name": {"type": "string"},
  "level": {"type": "number", "max": 1337}

Great. There are tools for that. Nothing new. But then you want to write some tests. What data are you gonna use? Are you going write some fixtures yourself? Create a mock object using some other library?

That's what this experiment is all about. I wanted to create such a validation tool which can use the same structure to create random fake sample data (better known as samples of fake-random demo-data).

And: Good news, everyone! It works*! The source lives in src/.

var ps = require('./prop_schema')
ps.sample({name: {type: "string"}, level: {type: "number", max: 1337}})
// => { name: 'lorem lor', level: 1278 } 

* Sometimes, for some cases.

What does it have to do with React.js?

I'm so glad you asked. You see, React.js has this little, often overlooked feature called Prop Validation. It's used during development to validate the data in your component's properties. By default, React has some nice helper methods that should get you started, e.g. React.PropTypes.string.isRequired.

But the thing is, you can easily create your own prop validators -- they are just functions that get the props and output some warning to the console.

So, of course I had to take the glorious library described above and use it to create a new validation module. I'll call it ReactProps for now. Then, to spice things up a bit, let's give each validator an additional method called fake.

You can access a React component's original propTypes using component.originalSpec.propTypes (at least in React 0.10, this is probably a private API). Using this, it is trivial to call each propType's .fake() method and generate a new data set for your test component.

Complete Example

See also the CoffeeScript source of the complete profile example.

var React = require('react');
var ReactProps = require('./src/react_props');
var Person = React.createClass({
  // This is the important bit 
  propTypes: {
    name: ReactProps.require({
      first: {type: 'string', min: 1, max: 42, pattern: 'Name.firstName'},
      last: {type: 'string', min: 1, max: 42, pattern: 'Name.lastName'}
    age: ReactProps.require({type: 'number', min: 21, max: 42}),
  render: function () {
    return React.DOM.article({key: 0, className: 'person'}, [
      React.DOM.h1({key: 0, className: 'name'}, [
        "Dr. ",, " ",
      React.DOM.p({key: 1, className: 'age'}, ["Age: ", this.props.age])
var fakePerson = ReactProps.fake(Person, {key: 0}, []);
React.renderComponent(fakePerson, document.getElementById('container'));

Also note that elements with type: string support a special pattern property which can be set to a valid faker.js method (e.g. ''), which will then be used to generate the fake data.

Precise Validation Error

Imaging we use the example Person component from above with the following props:

Person({key: 0, age: -1, name: {first: 42}}, []);

It is obvious, that neither age nor name are valid. But what exactly is wrong with them? Here is the console output you get in development mode:

Invalid prop age supplied to Person: ["-1 should at least be 21"] [CheckError]

Invalid prop name supplied to Person: ["42 is not a string.", "last is required but not in [object Object]"] [Array[1], CheckError]

(The arrays at the end of the lines contain the actual, nested JS Errors that can be inspected in developer tools like Chrome's inspector and that contain further information, like a reference to the value that failed to validate.)

Getting this Experiment Started

Uses gulp and browserify, but you don't have to concern yourself with that. If you enjoy fiddling with that kind of stuff, though, I hope you enjoy reading it. I spend at least an hour to get it working (generating two JS files, one for my JS and one for external libraries).

$ npm install
$ npm run compile # or `build` to skip uglify and add sourcemaps 
$ open build/index.html # works on os x at least 

Now you should see a boring page that displays some random data on each reload using the not-so-boring idea described above.

You can use npm run watch to automatically recompile stuff when you change some files.

Run the Tests

I wrote some tests to determine that the validator/faker works as expected.

Believe it or not, I even wrote an amazing new test utility for this. I'll probably call it 'try-catch-foreach' or something and will replace it with mocha later on.

Run the tests with:

$ npm test

Code Style

Uses CoffeeScript and lodash, because then I can get stuff done wicked fast.

Further Ideas

  • Integrate more sophisticated random data using faker.js and a pattern attribute
  • See all the TODOs in the code.

Prior Art/Inspiration