Zan is a drop in replacement for React.PropTypes:

import { types } from 'zan';
React.createClass({
  propTypes: {
    name: types.string,
    age: types.number.isOptional
  },
  render() {/*...*/},
});

The primary differences between Zan and React.PropTypes are:

1. Checks are isRequired by default and expose an isOptional property
2. Provides an exactShape type checker
3. Provides introspection methods
4. Provides methods to help you create your own type checkers

Exposes all the same type-checkers as React.PropTypes. Each type-checker is required by default and has the following properties:

• isOptional - Returns an optional type checker. Optional checkers behave like React.PropType's default behavior.

• inspectArgs() - Returns the arguments passed to the type-checker creator.

  Example: shape(o).inspectArgs() === o

• inspectType() - Returns the checker type.

  Example: shape(o).inspectType() === shape.

• inspectIsOptional() - Return whether or not the checker is optional

  Example: shape(o).inspectIsOptional() === false.

  Example: shape(o).isOptional.inspectIsOptional() === true.

Like shape(), but disallows unrecognized keys.

Validates value against a type checker. Useful when using Zan outside of React components. Returns null if the data validates successfully or an Error object if there's an error:

Error: Invalid prop `value.field[0].subField` of type `object` supplied to `label`, expected an array.

Usage:

// Normal
const error = zan.check(type, value, 'label');
// Curried
const check = zan.check(type);
const error = check(value, 'label');

Allows you to create your own type checker. Here's how you'd create a checker that validates that data is an instance of a RegExp:

const regex = zan.createCustomChecker((props, propName /*, ...*/) => {
  const value = props[propName];
  if (!(value instanceof RegExp)) {
    return new Error('Expected a regex but found "' + (typeof value) + '".');
  }
});
// regex gets all of Zan's built-in goodness:
regex.isOptional;
regex.inspectType() === regex;

The checker is passed all the same arguments as React PropType checkers: props, propName, componentName, location, and propFullName.

The final checker errors will be in one of two forms:

Required prop `field.subField[0].name` was not specified in `MyComponent`.
Invalid prop `field.subField[0].name` of (type `number` OR value `xyz`) supplied to `MyComponent`...

If you return an error that doesn't start with Required or Invalid then Zan prefixes the error message with:

Invalid prop `field.subField[0].name` of value `xyz` supplied to `MyComponent`:

This is like createCustomChecker() but is for checkers that require arguments:

const range = zan.createCustomCheckerCreator((min, max) =>
  (props, propName/*, ...*/) => {
    const value = props[propName];
    if (value < min || value > max) {
      return new Error('Expected number in range `' + min + '` to `' + max + '`.');
    }
  }
);
// regex gets all of Zan's build-in goodness:
range(1, 3).isOptional;
range(1, 3).inspectType() === range;

Converts native arrays and objects to arrayOf() and shape() calls, so you don't have to:

import { types, recursive } from 'zan';
const { number, string } = types;

const propTypes = recursive({
  myAge: number,
  myFavoriteNumbers: [number],
  treeNode: {
    value: number
  },
  buddies: [{
    name: string,
    age: number,
  }],
});

// ...is equivalent to:

const propTypes = {
  myAge: number,
  myFavoriteNumbers: arrayOf(number),
  treeNode: shape({
    value: number,
  }),
  buddies: arrayOf(shape({
    name: string,
    age: number,
  })),
};

see test.js from more usage