Handlebars.js used in Open Event Web App

I recently started working in the Open Event Webapp project. One of the initial issues that I took up was a trivial UI bug. It was about adding sponsor names beneath sponsor images for better representation. The issue can be found here. On reading up the code base and exploring the project a bit, I came across a new template – Handlebars.js. Handlebars is a template which has it’s base with the Mustache templating language. One of the early discoveries that I made with Handlebars.js was the use of {{ }} and {{{ }}} and the basic difference between them. In general, all Handlebar.js expressions, just like in Mustache templating, are written between {{ }} or {{{ }}} type of brackets. That is how I learned to identify and distinguish Handlebars from core HTML, even though they are inter-linked. The official Handlebars documentation describes Handlebars expressions in the following way:

A handlebars expression is a {{, some contents, followed by a }} ”

Getting started with Handlebars.js


For a basic Linux installation, type the following in your command line:

npm install --save handlebars

Including Handlebars in HTML:

<script src="handlebars-v4.0.10.js"></script>

Handlebars templates are often stored in .hbs files for better readability and accessibility. The Open Event Webapp project consists of a handlebars .hbs file for each of the tracks, events, rooms, schedule, sessions and speakers templates. These can be found here, that is under src/backend/templates folder.

Difference between {{ }} and {{{ }}}: 

Handlebars enables developers to print raw HTML tags or code with the help of {{{ }}}. On the contrary, if you don’t want to print HTML (which is usually the case), use {{ }}. For better understanding, let’s take an example.

If our JS has an object that looks something like:

$(function () {
   var templateScript = $("#title-template").html();

   var temp = Handlebars.compile(templateScript);

var Title= {
“title”: <a> Handlebars</a>

Then, HTML of the following kind will help to distinguish the {{ }} and {{{ }}} brackets.

<script id=”title-template” type=”text/x-handlebars-template”>

//the first line will contain an anchor tag with the name “Handlebars”
//the second line will contain “<a>Handlebars</a>”

Block helpers in Handlebars:

Block helpers are identified by a ‘ #’ and they help to define and access custom iterators.

Handlebars allow calling JavaScript functions with the help of ‘helpers’. It doesn’t allow direct JavaScript code in the HTML with templates. We can create our own helpers using Handlebars.registerHelper () in our JavaScript. We generally pass a function to the helper. A good example was provided in the Handlebars.js documentation:

Handlebars.registerHelper('noop', function(options) {
  return options.fn(this);

By default, Handlebars helpers take the current context as the context to pass(“this”). Other fields are overshadowed. Incase, we want to access one of the fields that is masked by the default “this” context, we have to use a path reference.

Iterations using helpers:

Helpers can be a great way  to iterate over lists or objects. I will demonstrate it with an example from the Open Event Webapp project. To display all the sponsors of an event in the home page of the event Webapp, we use the following handlebars code, where we iterate over the object list “sponsorpics” that we have. It looks something like this:

{'1': ['Oreilly', 'Amazon'], '2': ['Huawei', 'Google'],'3': ['RedHat', 'GitHub']}
{{#if eventurls.sponsorsection}}
<div class="sponsor-container">
       <section class="sponsorscont">
         <div class="row sponsor-row">
           <div class="col-sm-12 col-md-12 col-xs-12 text-center">
             <h1 class="section-header">Proudly supported by</h1><br>
         <div class="row">
           <div class="col-sm-10 col-sm-offset-1">

             <div class="row">
               {{#each sponsorpics}}
                 {{#each this}}
                   <div class="{{{divclass}}}">
                     <div class=" {{{sponsorimg}}} text-center">
                       <a href="{{{url}}}" data-toggle="tooltip" title="{{{type}}}">
                         <img class="lazy centre {{{imgsize}}}" alt="{{{name}}}" data-original="{{{logo}}}">
             </div> <!-- sponsor-row -->

For your reference, you can view a sample Webapp for the OSCON 2017 event here.
For further information, please refer to Handlebars.js .
An interesting tutorial about Handlebars in 10 mins or less can be found here.

Using Partial in Handlebars and Reusing Code

Open Event Webapp uses handlebar partials for optimizing code. We can reuse a template using Handlebars partial.

How to use Handlebars partial ?

To use Handlebars partial, we have to follow some easy steps:

Step 1: In the .hbs file containing code, register your partial by using function Handlebars.registerPartial 

Handlebars.registerPartial('myPartial', '{{name}}')

Step 2: Calling the partial

{{> myPartial }}

In Open-Event Webapp we have made partials for common templates like navbar and footer.

1. // Navbar template (navbar.hbs)

 <!-- Fixed navbar -->
 <nav class="navbar navbar-default navbar-fixed-top">
  <div class="container">
   <div class="navbar-header navbar-left pull-left">
    <a class="navbar-brand" href="{{ eventurls.main_page_url }}">
    {{#if eventurls.logo_url}}
    <img alt="{{eventurls.name}}" class="logo logo-dark" src="{{  eventurls.logo_url }}">
    {{ eventurls.name }}
 <div class="navbar-header navbar-right pull-right">
   <ul style="margin-left:20px" class="nav navbar-nav pull-left">
   {{#if show}}
    <li class="pull-left"><a href="{{link}}" style="padding-right:0; padding-left:0;margin-left:15px"><i class="fa fa-lg fa-{{icon}}" aria-hidden="true" title="{{{icon}}}"></i></a></li>
 <button type="button" class="navbar-toggle" data-toggle="collapse" data-target=".navbar-collapse" style="margin-left:1em;margin-top:1em;">
   <span class="sr-only">Toggle navigation</span>
   <span class="icon-bar"></span>
   <span class="icon-bar"></span>
   <span class="icon-bar"></span>

 <div class="hidden-lg hidden-md hidden-sm clearfix"></div>
   <div class="collapse navbar-collapse">
    <ul class="nav navbar-nav navbar-right">
     <li class="navlink"><a id="homelink" href="index.html">Home</a>
     {{#if timeList}}
     <li class="navlink">
     <a id="schedulelink"href="schedule.html">
     {{#if tracks}}
     <li class="navlink">
      <a id="trackslink" href="tracks.html">Tracks</a>
     {{#if roomsinfo}}
     <li class="navlink">
      <a id="roomslink" href="rooms.html">Rooms</a>   
    {{#if speakerslist}}
    <li class="navlink">
      <a id="speakerslink" href="speakers.html">Speakers</a>
//Compiling Template by providing path

2. const navbar = handlebars.compile(fs.readFileSync(__dirname + '/templates/partials/navbar.hbs').toString('utf-8'));
// Register Partial

3. handlebars.registerPartial('navbar', navbar);

Templating with Handlebars and Nodejs

There are many frameworks present today that does DOM manipulation. But, DOM manipulation is useful only with simpler Javascript apps. If we want to deal with huge amount of data, we will need to take the support of templating.

One of the templating libraries is Handlebar.js. Handlebars.js is the lightest and one of the fastest templating libraries I have worked with.

How to work with Handlebars ?

Handlebars can be said as the superset of Mustache templating language. In Open-event-web app, Handlebars is used along with Node.js.

1. To install Handlebars
npm install handlebars
2. To include handlebars
const handlebars = require('handlebars');
const fs         = require('fs-e'xtra);
3. To compile a file ( Extension .tpl or hbs)
const tpl = handlebars.compile(fs.readFileSync(__dirname +   '/templates/schedule.hbs').toString('utf-8'));
fs.writeFileSync(distHelper.distPath + '/' + appFolder + '/tracks.html', tpl(jsonData));

Here jsonData is the JSON Array of objects provided to the template.

An example of a .hbs templating file can be :

 <div class="track-names col-md-2">
 {{# tracks}}
 {{#if title}}
 <ul class="title-inline">
 <li style="background-color:{{{color}}}" class="titlecolor"></li>



Twitter Section Using loklak webtweets

In Open event web app, the user can provide URL of social links such as Twitter, Facebook etc in the event.json file inside the ZIP. The previous functionality was to use Twitter API and to generate a timeline showing the tweets of the twitter URL mentioned in event.json by user. But, it can be done by following another approach which reduces the third party dependency i.e Loklak-webtweets.

I have implemented the twitter section using loklak webtweets which can be done very easily.

Step 1:  Including necessary files from loklakwebtweets repository inside index.html. You can find them in js/ folder of this repository.

<script src="./dependencies/jquery.min.js"></script>
<script src="./dependencies/bootstrap.min.js" type="text/javascript"></script>
<script src="./dependencies/loklak-fetcher.js" type="text/javascript"></script>
 <script src="./dependencies/tweets.js" type="text/javascript"></script>


Step 2:  Specify the data source in HTML from which twitter data will be fetched. Here I have extracted the last word from the twitter URL provided by the user and passed it to HTML.

const sociallinks = Array.from(event.social_links);
 var twitter ="";
 sociallinks.forEach((link) => {
  if(link.name.toLowerCase() === "twitter") {
   twitter = link.link;
 const arrayTwitterLink = sociallink.split('/');
 const twitterLink = arrayTwitterLink[arrayTwitterLink.length - 1];
 const urls= {
   twitterLink: twitterLink,
   tweetUrl: twitter,

This code will search twitter link in social links array present in event.json and get its last character which will be provided to data-from and data-query attribute of HTML.

 <section class="sponsorscont">
  <div class="tweet-row">
   <div class="col-sm-12 col-md-12 col-xs-12">
    <i class ="social_twitter fa fa-twitter"></i>
     <div class="tweets-feed" id="tweets" data-count=50 data-query="    {{{eventurls.twitterLink}}}" data-from="{{{eventurls.twitterLink}}}">
     <div class="arrow-up"></div>
      <p id="tweet" class="tweet">
   <span style="margin-bottom: 20px;" id="dateTweeted"></span>
    <b><a href="{{eventurls.tweetUrl}}"/>
    </b></u> for more updates</p> 

Step 3 : Now we just need to add styling so that it looks decent. For that, I have written some SASS.

.tweets-feed {
   color: $black;
   line-height: 30px;
   font-size: 20px;
   transition: opacity 0.2s linear;
   margin-bottom: 20px;
   height: 100px;
  a {
   color: $black;
   text-decoration: underline;
   font-weight: 700;

  #dateTweeted {
   font-size: 15px;
   display: block;


.tweet-row {
   padding: 0 80px;
   margin-bottom: 80px;
   .social_twitter {
     font-size: 60px;
     margin-bottom: 12px;

The output from the above code is a well designed Twitter section fetching tweets from the URL provided as a string in event.json by user.



Responsive Image Overlay

Image overlay is a very common concept in front-end development. It is easy to implement but difficult when we deal it with different screen sizes, where we need to cover the image with the overlay each time the screen size is changed. I have gone through various blog posts when I need to implement the same for Open-event webapp and researched a solution that works for all screen sizes without any media query.


How to add an overlay to an image ?

If we need four images in a single row nearly 300*300px.  The code below shows the markup.

image-holder : The parent class to take the image and overlay inside it.

background-image: This class takes image source.

responsive-overlay: This is the key point to make it responsive. Responsive-overlay contains a class hover-state to add overlay absolutely and a class social-links.

social-links: It adds content to hover-state.


<div class="image-holder">
  <img class="background-image" alt="" src="">
   <div class="responsive-overlay">
     <div class="hover-state text-center preserve3d">
       <div class="social-links vertical-align">


The styling is written with SASS in .scss file as shown below.

//overlayimage and backgroundshade can be set in config.scss

 .image-holder {
   position: relative;
   overflow: hidden;
   margin-bottom: 12px;

   .background-image {
     height: 300px;
     width: 300px;
     display: block;
     margin: 0 auto;
     background-color: $background-shade;
   .responsive-overlay {
     @include responsiveoverlay;

    .preserve3d {
       height: 300px;

    .hover-state {
     @include hoverstate;
     height: 300px;
     width: 300px;

  @mixin responsiveoverlay {
     height: 100%;
     position: absolute;
     top: 0;
     width: 100%;

   @mixin hoverstate {
     background: $overlayimage;
     display: block;
     height: 300px;
     left: 0;
     margin: 0 auto;
     opacity: 0;
     position: relative;
     top: 0;
     -moz-transition: all 0.3s ease-out;
     -webkit-transition: all 0.3s ease-out;
     transition: all 0.3s ease-out;
     width: 300px;
     z-index: 2;

This code will work for responsiveness as well. The main catch here is the responsive-overlay class which is made 100% in width but set to position absolute. The images which are 300 * 300 px in size will take an overlay of the same size because of hover-state class. Instead, if we adjust sizes of images in small screens the above code will adjust overlay on the image automatically.

Like, on tablets we can have an overlay like this.


And on mobile screen output is like that :



Responsiveness is easy if we follow correct concepts. Here, the concepts of absolute and relative positioning in CSS have done the magic. Now we can play by adding different contents and effect on hover following the same basics.

Optimizing page load time

The average size of a web page has been growing at an accelerating rate over the last few years. Last week, when the open-event webapp was tested, it was very slow to load because of loading 67.2 MB data ( which contained audio and image files ) on the web page.I have taken following steps which are good to read to make any web application load faster.

1. Stop preloading of audio files

The HTML5 audio player loads all audio files by default on the page. To stop this we have to change the code as

<audio controls preload="none">
 <source src="{{audio}}" type="audio/mpeg">

Setting preload option to none help us to load audio only when it is clicked. Hence it decreases the HTTP calls and decreases the page loading time.


Network tab with Audio files takes 68.0MB  load and 13.6 minute loading time.




Network tab with option <audio controls preloaded=”none”> takes 1.1 MB load and  1 minute loading time. This was a huge improvement but more optimizations can be done.

2. Using Compression Middleware

Express compression middleware works like a charm by compressing the response coming to the web page. It is too simple to add.

$ npm install compression
var compression = require('compression')
var express = require('express')

var app = express()

// compress all requests

// add all routes

This has compressed the responses and decreased the page load time.

3.  Reduce the number of HTTP requests

Another great way of speeding up your web pages is to simply reduce the number of files that need to be loaded.

Combine files

Combining multiple stylesheets into one file is a really useful way of eliminating extra HTTP requests. This strategy can also be adopted for your JavaScript files. A single larger CSS or JavaScript file will often load quicker because more time can be spent downloading the data rather than establishing multiple connections to a server.

After such optimizations, the webapp loads now in 8-15 seconds with DOM loaded in 2 seconds.


The result of these optimizations are awesome. We can test the page speed by using various tools like pagespeed, speedtracer etc.

Self-Contained Folder For Webapp

The first version of Open-event-webapp will be a generator that will create the web app.

This week I have worked on various OTS issues that will become the basis for the web app. The OpenTechSummit web app works along with Open-event-scraper.

The web app can be generated in any empty repository and can be hosted with gh-pages by just running build.sh  file from the Open-event-scraper. This is the build.sh file I have written for doing this.

build file


How can you create the webapp from scraper in your repository ?


1 . Replace the URL of the repository in git clone command.

git clone – – depth=1 < destination repo url > ots-repo

2 . Run the file build.sh from  Open-event-scraper.



Utility for transferring content using build.sh


The build.sh file is written to make a folder that is self-sufficient. It means it can be taken anywhere and it should work on its own.

The build.sh file first creates a clone of the destination repository in the local Open-event-scraper. It itself make the required folders inside the cloned repository and runs generator.js which provides index.html file according to the template schedule.tpl. The resync command that is known as remote sync is used to transfer the files remotely. A programm folder is created automatically that includes all the CSS, JS,  JSON and other important files used to run the web app.

Finally, the programm folder along with all necessary files is pushed to gh-pages branch of the destination repository.

Working Example


To create the web app I have replaced the destination URL as shown in the image.


After running the build.sh we will get the output as shown :

1 .

Programm folder ( self-sufficient)


Sub folders inside Programm folder

That’s how a folder is generated which contains all the necessary files needed to run the web app.

Open Source Event App Development

Some background about myself, I am a 3rd year Information Technology student from JSS Academy of Technical Education, Noida, India. I love Front-end development and is currently working on an awesome project Open-Event .

The project will make it easier for the events, tech summits to create a web app and mobile app quickly by providing necessary information such as speakers for the event, sessions, tracks, location etc. The project itself consists of three core components :
1. Open-Event Organiser Server
2. Open-Event Android App
3. Open-Event Web app
It’s the end of community bonding period before the past week, which was the best time to get ourselves familiar with the practices of the community, understanding of the codebase, making new friends and setting up goals. I have already set up my goals and is working on Open-event-web app.

The first version of the web app is to make the web app functional by just uploading a JSON file, the second part is to make it sync with the REST API provided by the Orga-server. I with Arnav have created the User-Story for the web app. Also, I have created the data-flow for the work, we will be carrying forward.

I am having a good time, and will work hard to complete the goals of the project.