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3.5.0 • Public • Published

Bellhop Actions Status Dependency Status

Bellhop is a simple event-based communication layer between the page DOM and an iframe. It doesn't require any additional dependencies. Super easy to use and setup.


npm install bellhop-iframe

Importing Bellhop

The Bellhop module contains support for ES6 modules, CommonJS and browser global definitions. To import with ES6,

import { Bellhop } from 'bellhop-iframe';

To import with CommonJS, refer instead to the UMD build

const Bellhop = require('bellhop-iframe/dist/bellhop-umd.js');

You can also import the UMD version by using import

import { Bellhop } from 'bellhop-iframe/dist/bellhop-umd.js'

Lastly, the UMD module can also be directly included on an HTML page. This will declare Bellhop and attach it directly to window

<script src="node_modules/bellhop-iframe/dist/bellhop-umd.js"></script>

Basic Usage

Here's a very simple example to get started. We have two pages index.html and child.html. This is the minimum you need to get them talking to each other.

Contents of index.html

<iframe src="child.html" id="page" width="200" height="200"></iframe>

// Create the bellhop object
const bellhop = new Bellhop();

// Pass in the iframe DOM object

// Listen for the 'init' event from the iframe
bellhop.on('init', function(event){
  // Handle the event here!

// Send data to the iframe
bellhop.send('user', {
  "name" : "Dave Smith",
  "age" : 16,
  "city" : "Boston"

Contents of child.html


// Create the bellhop object
const bellhop = new Bellhop();

// An example event to sent to the parent

// Handle events from the parent
bellhop.on('user', function(event){
  // Capture the data from the event
  const user =;

Available Methods

new Bellhop

The constructor creates a new Bellhop instance, taking an optional unique identifier for this instance. If no id is provided, a random one is selected


Connects a Bellhop instance to an iframe, or it's containing window. For instance, given a Bellhop instance bellhop:


will connect a child iframe to it's parent, allowing it to emit messages out of the iframe. However,

var iframe = document.querySelector('iframe');

allows a containing page to connect with an interior iframe and emit message into the iframe.


disconnect removes any listener for events from another frame, and stops listening for messages altogether


Removes an event listener previously added by the .on() method, or removes a given callback method from a listener. When deleting a callback, the function passed in is required to be the original function passed into the .on() method.‘init’); // removes the listener ‘init’ and all callbacks assigned to it‘init’, callback) // removes the specific callback provided without removing the listener


Sends a named message to another iframe:

bellhop.send('newHighscore', { value: 100 });

fetch and respond

Convenience methods for automating response of values between the interior and exterior of frames. For instance:

// index.html
var iframe = document.querySelector('iframe');
var bellhop = new Bellhop(iframe);
bellhop.respond('config', { difficulty: 'hard', theme: 'dark' });

// child.html
var bellhop = new Bellhop();
bellhop.fetch('config', function(result) {
  console.log(result); // { difficulty: 'hard', theme: 'dark' }

Additionally, object passed to respond() can be a function, whose result will be returned in the callback of the fetch function.

// index.html
var functionExample = function(){
  return "result of functionExample";
bellhop.respond('function', functionExample);

// child.html
bellhop.fetch('function', function(result) {
  console.log(; //result of functionExample

Furthermore, respond() accepts a plain object, string, or number. If a function is passed, it will be called and the function's return-value sent. If a promise is passed in or returned from a function that was passed in, that promise will be await-ed before it's value returned.

For example, the following all return "data" to bellhop.fetch()

bellhop.respond('example', "data");

//OR  (promise example)
let promiseData = new Promise(function(resolve, reject) {
bellhop.respond('example', promiseData)

//OR  (function example)
var functionExample = function(){
  return "data";
bellhop.respond('example', functionExample);

//OR (function that returns a promise)
var functionPromiseExample = function(){
  return new Promise(function(resolve, reject) {
bellhop.respond('example', functionPromiseExample);


Triggers any event handlers for a given event type optionally passing data to other areas in the app that are listening for this event

bellhop.trigger('eventType', {data: 'example'}); // triggers the event 'eventType' passing data to it's handlers

Debug Mode

Bellhop has a debug mode which enables additional logging when an instance sends or receives a message. It can be enabled by simply setting the debug flag to true:

bellhop.debug = true;

By default (above method) it will print a message outlining whether the bellhop instance was a child or parent, whether the message was sent or received, and the contents of the message. If you require additional or custom logging you can also pass a function as the flag.

const log = () => {console.log('Hello World!');}
bellhop.debug = log; // Hello World!

If you pass a function to debug three parameters* are passed to help fill out the log statements if required:

const log = ({isChild, received, message}) => {
  console.log(isChild); // (boolean) whether the instance is a child or parent.
  console.log(received); // (boolean) whether the instance has received a message or sent one.
  console.log(message); // (object) the content of the message.

*Note: the names must be identical, but you are able to omit any or all if they're not required.


Property for retrieving the iframe element through which this Bellhop instance is communicating:

var iframe = document.querySelector('iframe');
var bellhop = new Bellhop(iframe);

console.log( === iframe.contentWindow); // true


Copyright (c) 2021 Springroll

Released under the MIT License.

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