react-native-webview-bridge/scripts/webviewbridge.js

(function (window) {
  'use strict';

  //Make sure that if WebViewBridge already in scope we don't override it.
  if (window.WebViewBridge) {
    return;
  }

  var RNWBSchema = 'wvb';
  var sendQueue = [];
  var receiveQueue = [];
  var doc = window.document;
  var customEvent = doc.createEvent('Event');

  function callFunc(func, message) {
    if ('function' === typeof func) {
      func(message);
    }
  }

  function signalNative() {
    window.location = RNWBSchema + '://message' + new Date().getTime();
  }

  //I made the private function ugly signiture so user doesn't called them accidently.
  //if you do, then I have nothing to say. :(
  var WebViewBridge = {
    //this function will be called by native side to push a new message
    //to webview.
    __push__: function (message) {
      receiveQueue.push(message);
      //reason I need this setTmeout is to return this function as fast as
      //possible to release the native side thread.
      setTimeout(function () {
        var message = receiveQueue.pop();
        callFunc(WebViewBridge.onMessage, message);
      }, 15); //this magic number is just a random small value. I don't like 0.
    },
    __fetch__: function () {
      //since our sendQueue array only contains string, and our connection to native
      //can only accept string, we need to convert array of strings into single string.
      var messages = JSON.stringify(sendQueue);

      //we make sure that sendQueue is resets
      sendQueue = [];

      //return the messages back to native side.
      return messages;
    },
    //make sure message is string. because only string can be sent to native,
    //if you don't pass it as string, onError function will be called.
    send: function (message) {
      if ('string' !== typeof message) {
        callFunc(WebViewBridge.onError, "message is type '" + typeof message + "', and it needs to be string");
        return;
      }

      //we queue the messages to make sure that native can collects all of them in one shot.
      sendQueue.push(message);
      //signal the objective-c that there is a message in the queue
      signalNative();
    },
    onMessage: null,
    onError: null
  };

  window.WebViewBridge = WebViewBridge;

  //dispatch event
  customEvent.initEvent('WebViewBridge', true, true);
  doc.dispatchEvent(customEvent);
}(window));