Experiment.js

var React = require('react-native');
var {
  AsyncStorage,
  PropTypes,
  View
} = React;

var Experiment = React.createClass({

  propTypes: {
    name: PropTypes.string.isRequired,
    children: ((props, propName) => {
      var children = props[propName];
      if (!Array.isArray(children) || children.length < 2) {
        return new Error('You must have at least 2 Variants.');
      }
      for (child of children) {
        if (!child.type.prototype.isVariant) {
          return new Error('One or more children is not a Variant.');
        }
      }
    }),
    choose: PropTypes.func,
    onChoice: PropTypes.func,
    onRawChoice: PropTypes.func
  },

  getDefaultProps() {
    return {
      choose(variants) {
        var choice = Math.floor(Math.random() * variants.length);
        return variants[choice];
      },
      onChoice(testName, variantName) { /* noop */ },
      onRawChoice(test, variant) { /* noop */ }
    }
  },

  getInitialState() {
    return {
      variant: <View/>
    }
  },

  componentWillMount() {
    this.variants = this.props.children;

    this.key = 'react-native-ab:Experiment:' + this.props.name;

    AsyncStorage.getItem(this.key, ((err, variantName) => {
      var choice;
      if (err || !variantName) {
        choice = this.props.choose(this.variants);
        AsyncStorage.setItem(this.key, choice.props.name); // Optimistic update
      }
      else {
        choice = this.getVariant(variantName);
      }
      this.props.onChoice(this.props.name, choice.props.name);
      this.props.onRawChoice(this, choice);
      this._onChange({
        variant: choice
      });
    }).bind(this));
  },

  render() {
    return this.state.variant;
  },

  getActiveVariant() {
    return this.state.variant;
  },

  getName() {
    return this.props.name;
  },

  getVariant(name) {
    return this.variants.find((v) => v.props.name == name);
  },

  reset(cb) {
    AsyncStorage.removeItem(this.key, cb);
  },

  _onChange(changed) {
    var newState = Object.assign({}, this.state, changed);
    this.setState(newState);
  }
});

module.exports = Experiment;