Ember Mixins used in Open Event Frontend

This post will illustrate how ember mixins are used in the Open Event Frontend to avoid code duplication and to keep it clean to reduce code complexity.

The Open Event application needs forms at several places like at the time of login, for the creation of the event, taking the details of the user, creating discount codes for tickets etc. Every form performs similar actions which taking input and finally storing it in the database. In this process, a set of things keep executing in the background such as continuous form validation which means checking inputted values to ensure they are correctly matched with their type as provided in the validation rules, popping out an error message in case of wrong inputted values, etc. which is common to all the forms. The only thing which changes is the set of validation rules which are unique for every form. So let’s see how we solved this issue using Ember Mixins.

While writing the code, we often run into the situation where we need to use the similar behaviour in different parts of the project. We always try not to duplicate the code and keep finding the ways to DRY ( Don’t Repeat Yourself ) up the code. In Ember, we can share the code in the different parts of the project using Ember.Mixins.

While creating the forms, we mostly have differing templates but the component logic remains same. So we created a mixin form.js which contains all the properties which are common to all the forms. The code mixin contains can be reused throughout different parts of the application and is not a concern of any one route, controller, component, etc. The mixins don’t get instantiated until we pass them into some object, and they get created in the order of which they’re passed in. The code for form.js mixin looks like this.

export default Mixin.create({
  autoScrollToErrors : true,
  autoScrollSpeed    : 200,

  getForm() {
    return this.get('$form');
  },

  onValid(callback) {
    this.getForm().form('validate form');
    if (this.getForm().form('is valid')) {
      callback();
    }
  },
  
  didRender() {
      const $popUps = this.$('.has.popup');
      if ($popUps) {
        $popUps.popup({
          hoverable: true
        });
      }
      let $form = this.$('.ui.form');
      if ($form) {
        $form = $form.first();
        if (this.get('getValidationRules') && $form) {
          $form.form(merge(defaultFormRules, this.getValidationRules()));
        }
      },
  didInsertElement() {
    $.fn.form.settings.rules.date = (value, format = FORM_DATE_FORMAT) => {
      if (value && value.length > 0 && format) {
        return moment(value, format).isValid();
      }
      return true;
    };
  }

The complete code can be seen here.

Let’s start understanding the above code. In the first line, we created a mixin via Ember.Mixin.create() method. We have then specified the property ‘autoScrollToErrors’ to true so in case if there is some error, the form will automatically scroll to the error. The property ‘autoScrollSpeed’ specifies the speed with which the form will auto scroll to show the error. ‘getForm()’ method helps in getting the object which will be passed to the mixin. In ‘onValid()’ method we’re validating the form and passing the callbacks if it is correctly validated. We then have ‘didRender()’ method which renders the popups, checkboxes and form rules. The popups help in showing the errors on the form. In this method, we’re fetching the validation rules which are written in child/subclasses which are using this mixin to create the form.  The validation rules help in validating the form and tells if the value inputted is correct or not. In most of the forms, we have a field which asks for some specific date. The piece of code under ‘didInsertElement()’ helps in validating the date and returns true if it is correct. We have ‘willDestroyElement()’ method which destroys the popup if the window is changed/refreshed.

Let see the use case of the above form mixin. At the time of login, we see a form which asks for the user’s credentials to validate if the user is already registered or not. To create that login form we use form mixin. The code for login-form.js looks like this.

export default Component.extend(FormMixin, {
getValidationRules() {
  
fields : {
        identification: {
          identifier : 'email',
          rules      : [
            {
              type   : 'empty',
              prompt : this.l10n.t('Please enter your email ID')
            },
            {
              type   : 'email',
              prompt : this.l10n.t('Please enter a valid email ID')
            }
          ]
        },
        password: {
          identifier : 'password',
          rules      : [
            {
              type   : 'empty',
              prompt : this.l10n.t('Please enter your password')
            }
          ]
        }
      }
   }
});

The complete code can be found here.

We can see that in above code we are creating the form by extending our FormMixin which means that the form will have all the properties which are part of mixin along with the properties which remain unique to this class. Since the validation rules remain unique per form so we’re also providing the rules (easy to comprehend) which will help in validating the fields.

This is how our forms look like after and before applying validation rules.

Fig. 1: Login form before applying validation rules

          Fig. 2: Login form after applying validation rules

To sum it up, we can say that mixins are of great use when we want to keep our code DRY or reduce the code duplication. It helps in removing the unnecessary inheritance keeping it short. The code written using mixin is lesser complex and easily understandable.

References:

Know the Usage of all Emoji’s on Twitter with loklak Emoji Heatmap

Loklak apps page now has a new app in its store, Emoji Heatmap. This app can be used to see the usage of all the emoji’s in the tweets all over the world in the form of heatmap. So, the major difference between the emoji heatmap and emoji heatmapper apps are heatmapper shows the tweets related to specific search query whereas this heatmapper app, it displays all the tweets which contains emojis.

How do the App fetches and stores the locations

The emoji heatmap uses the loklak search API . The search API needs a query in order to search and output the JSON data. But this app takes no input from the user end to search any query. To make the search dynamic, we are using an existing JSON file from emojiHeatmapper app and loklak-fetcher-client javascript file. From the emoji.json file, we collect the each query item and search it using loklak-fetcher-client. The output json file which we get from loklak-fetcher-client is retrieved into the emojiHeatmap and we extract the location parameter. The location parameter is then stored into the “feature” option of open layers 3 maps.

So, here in the emoji Heatmap app, we iterate over the emoji.json, get different search query each time when we search for it using loklak search API.

Code which adds the location retrieved into feature

  $.getJSON("../emojiHeatmapper/emoji.json", function(json) {
    for (var i = 0; i < json.data.length; i++){
      var query = json.data[i][1];
      // Fetch loklak API data, and fill the vector
      loklakFetcher.getTweets(query, function(tweets) {
        for(var i = 0; i < tweets.statuses.length; i++) {
          if(tweets.statuses[i].location_point !== undefined){
          // Creation of the point with the tweet's coordinates
          //  Coords system swap is required: OpenLayers uses by default
          //  EPSG:3857, while loklak's output is EPSG:4326
            var point = new ol.geom.Point(ol.proj.transform(tweets.statuses[i].location_point, 'EPSG:4326', 'EPSG:3857'));
            vector.addFeature(new ol.Feature({  // Add the point to the data vector
              geometry: point,
              weight: 20
            }));
          }
        }
      });
    }
  });

 

The above function gets has two variables query and point. The query variable stores the data that is being retrieved from the emoji.json file each time it iterates and that query is being sent into the loklak-fetcher-client. Then the point variable is in which the location tracked using the loklak search API is converted into the co-ordinates system followed by the Open Layers 3. Then the point is added as a feature to the map vector. The map vector is the place where all the features are stored and then appended onto the map as a heatmap.

Resources

Implementing Sponsors API in Open Event Frontend to Display Sponsors

This article will illustrate how the sponsors have been displayed on the public event page in Open Event Frontend using the Open-Event-Orga sponsors API. As we know that the project is an ember application so, it uses Ember data to consume the API. For fetching the sponsors, we would be mainly focusing on the following API endpoint:

GET /v1/events/{event_identifier}/sponsors

 

In the application we need to display the sponsors is the event’s public page which contains the event details, ticketing information, speaker details etc. along with the list of sponsors so, we will be only concerned with the public/index route in the application. As the sponsors details are nested within the events model so we need to first fetch the event and then from there we need to fetch the sponsors list from the model.

The model to fetch the event details looks like this:

model(params) {
return this.store.findRecord('event', params.event_id, { include: 'social-links' });
}

 

But we can easily observe that there is no parameter related to sponsor in the above model. The reason behind this is the fact that we want our sponsors to be displayed only on the event’s index route rather than displaying them on all the sub routes under public route. To display the sponsors on the public/index route our modal looks like this:

model() {
    const eventDetails = this._super(...arguments);
    return RSVP.hash({
      event   : eventDetails,
      sponsors: eventDetails.get('sponsors')
   });
}

 

As we can see in the above code that we have used this._super(…arguments) to fetch the event details from the event’s public route model which contains all the information related to the event thereby eliminating the need of another API call to fetch sponsors. Now using the ember’s get method we are fetching the sponsors from the eventDetails and putting it inside the sponsors JSON object for using it lately to display sponsors in public/index route.

Till now, we’ve fetched and stored the sponsors now our next task is to display the sponsors list on the event’s index page. The code for displaying the sponsors list on the index page is

{{public/sponsor-list sponsors=model.sponsors}} 

 

The sample user interface without  for displaying the sponsors looks like this:  

Fig. 1: The sample user interface for displaying the sponsors

After replacing the real time data with the sample one, the user interface (UI) for the sponsors looks like this.

Fig. 2: The user interface for sponsors with real time data

The entire code for implementing the sponsors API can be seen here.

To conclude, this is how we efficiently fetched the sponsors list using the Open-Event-Orga sponsors API, ensuring that there is no unnecessary API call to fetch the data.  

Resources:

Customizing Serializers in Open Event Front-end

Open Event Front-end project primarily uses Ember Data for API requests, which handles sending the request to correct endpoint, serializing and deserializing the request/response. The Open Event API project uses JSON API specs for implementation of the API, supported by Ember data.

While sending request we might want to customize the payload using a custom serializer. While implementing the Users API in the project, we faced a similiar problem. Let’s see how we solved it.

Creating a serializer for model

A serializer is created for a model, in this example we will create a user serializer for the user model. One important thing that we must keep in mind while creating a serializer is to use same name as that of model, so that ember can map the model with the serializer. We can create a serializer using ember-cli command:

ember g serializer user

 
Customizing serializer

In Open Event Front-end project every serializer extends the base serializer application.js which defines basic serialization like omitting readOnly attributes from the payload.

The user serializer provides more customization for the user model on top of application model. We override the serialize function, which lets us manipulate the payload of the request. We use `snapshot.id` to differentiate between a create request & an update request. If `snapshot.id` exists then it is an update request else it is a create request.

While manipulation user properties like email, contact etc we do not need to pass ‘password’ in the payload. We make use of ‘adapterOptions’ property associated with the ‘save()’ method. If the adapterOptions are associated and the ‘includePassword’ is set then we add ‘password’ attribute to the payload.

import ApplicationSerializer from 'open-event-frontend/serializers/application';
import { pick, omit } from 'lodash';

export default ApplicationSerializer.extend({
  serialize(snapshot, options) {
    const json = this._super(...arguments);
    if (snapshot.id) {
      let attributesToOmit = [];
      if (!snapshot.adapterOptions || !snapshot.adapterOptions.includePassword) {
        attributesToOmit.push('password');
      }
      json.data.attributes = omit(json.data.attributes, attributesToOmit);
    } else if (options && options.includeId) {
      json.data.attributes = pick(json.data.attributes, ['email', 'password']);
    }
    return json;
  }
});

If we want to add the password in the payload we can simply add ‘includePassword’ property to the ‘adapterOptions’ and pass it in the save method for operations like changing the password of the user.

user.save({
  adapterOptions: {
    includePassword: true
  }
})

Thank you for reading the blog, you can check the source code for the example here.
Resources

Learn more about how to customize serializers in ember data here

Adding Event Overview Route in Open Event Frontend

In Open Event Frontend we have an event overview route which is like a mini dashboard for an event where information regarding event sponsors, general info, roles, tickets, event setup etc. is present. All of the information is present in their corresponding components and this dashboard is made up of those components. To create this dashboard we will first create its components.

To create a component we will use following ember command-

ember -g component <component-name>

This command will give us three files: a template, a component and a test file corresponding to that component. We will use this command to generate all our components.

Now let’s discuss each component separately and see how many of them are combined to form this route-

The event-setup-checklist component contains semantic ui’s steps to maintain checklist of basic-details, sponsors, session & microlocation, call for speakers, session and speakers form customization so that it becomes easy to identify which step is complete and which is not.

Next is general-info component which shows basic information about an event like start-time, end-time, location, number of speakers, number of sponsors etc. It also shows whether the event is live or not.

In manage-roles component, manage the role for a given person, add people and assign different roles to them, edit roles for different people. Also we can see who are invited for a given role and who accepted them.

In event-sponsors component we manage the sponsors for the event, edit an existing sponsor, add a new sponsor with their logo, name, type and level. Also we can delete an existing sponsor.

Next is the ticket component which displays the details of number of orders, number of tickets sold, and total sales. Also it displays the number of types of tickets are sold.

Next is our app-component which has two choices. First is to generate android app for the event and second is to generate webapp of the event.

And finally in our view.index template, we add these components using ui stackable grid layout. Whenever we want to conditionally show or hide a component, we can do that in our event.index template and hence it becomes very easy to manage huge amounts content on a single page.

Resources

File Upload Validations on Open Event Frontend

In Open Event Frontend we have used semantics ui’s form validations to validate different fields of a form. There are certain instances in our app where the user has to upload a file and it is to be validated against the suggested format before uploading it to the server. Here we will discuss how to perform the validation.

Semantics ui allows us to validate by facilitating pass of an object along with rules for its validation. For fields like email and contact number we can pass type as email and number respectively but for validation of file we have to pass a regular expression with allowed extension.The following walks one through the process.

fields : {
  file: {
    identifier : 'file',
    rules      : [
      {
        type   : 'empty',
        prompt : this.l10n.t('Please upload a file')
      },
      {
        type   : 'regExp',
        value  : '/^(.*.((zip|xml|ical|ics|xcal)$))?[^.]*$/i',
        prompt : this.l10n.t('Please upload a file in suggested format')
      }
    ]
  }
}

Here we have passed file element (which is to be validated) inside our fields object identifier, which for this field is ‘file’, and can be identified by its id, name or data-validate property of the field element. After that we have passed an array of rules against which the field element is validated. First rule gives an error message in the prompt field in case of an empty field.

The next rule checks for allowed file extensions for the file. The type of the rule will be regExp as we are passing a regular expression which is as follows-

/^(.*.((zip|xml|ical|ics|xcal)$))?[^.]*$/i

It is little complex to explain it from the beginning so let us breakdown it from end-

 

$ Matches end of the string
[^.]* Negated set. Match any character not in this set. * represents 0 or more preceding token
( … )? Represents if there is something before (the last ?)
.*.((zip|xml|ical|ics|xcal)$) This is first capturing group ,it contains tocken which are combined to create a capture group ( zip|xml|ical|ics|xcal ) to extract a substring
^ the beginning of the string

Above regular expression filters all the files with zip/xml/ical/xcal extensions which are the allowed format for the event source file.

References

  • Ivaylo Gerchev blog on form validation in semantic ui
  • Drmsite blog on semantic ui form validation
  • Semantic ui form validation docs
  • Stackoverflow regex for file extension

Keep updating Build status in Meilix Generator

One of the problems we faced while working Meilix Generator was to provide user with the status of the custom ISO build in the Meilix Generator web app so we came up with the idea of checking the status of the link generated by the web app. If the link is available the status code would be 200 otherwise it would be 404.

We have used python script for checking the status of URL. For generating URL, we use the tag name which will be used as a variable to generate the URL of the unique event user wants the ISO for and the date will help in generation of link rest of the link remains the same.

tag = os.environ["TRAVIS_TAG"]
date = datetime.datetime.now().strftime('%Y%m%d')
url=https://github.com/xeon-zolt/meilix/releases/download/"+tag+"/meilix-zesty-"+date+"-i386.iso"

 

Now we will use urllib for monitoring the status of link.

req = Request(url)
    try:
        response = urlopen(req)
    except HTTPError as e:
        return('Building Your Iso')
    except URLError as e:
        return('We failed to reach the server.')
    else:
        return('Build Sucessful : ' + url)

 

After monitoring the status the next step was to update the status dynamically on the status page.

So we’llll use a status function in the flask app which is used by JavaScript to get status of the link after intervals of time.

Flask :

@app.route('/now')
def status_url():
    return (status())

 

Javascript:

<script type ="text/javascript">
let url ="/now"
function getstatus(url)
{
    fetch(url).then(function(response){
        return response.text()
    }).then(function(text){
        console.log("status",text)
        document.querySelector("div#status")
        .innerHTML = text
    })
    }
window.onload = function(){
    fetch(url).then(function(response){
        return response.text()
    }).then(function(text){
        console.log("status",text)
        document.querySelector("div#status")
        .innerHTML = text
    })
    window.setInterval(getstatus.bind(null,url),30*1000)
}
/*setInterval(function,interval in millsecs)*/
</script>

 

This covers various steps to prompt user whether the build is ready or not.

Resource

Adding React based World Mood Tracker to loklak Apps

loklak apps is a website that hosts various apps that are built by using loklak API. It uses static pages and angular.js to make API calls and show results from users. As a part of my GSoC project, I had to introduce the World Mood Tracker app using loklak’s mood API. But since I had planned to work on React, I had to go off from the track of typical app development in loklak apps and integrate a React app in apps.loklak.org.

In this blog post, I will be discussing how I introduced a React based app to apps.loklak.org and solved the problem of country-wise visualisation of mood related data on a World map.

Setting up development environment inside apps.loklak.org

After following the steps to create a new app in apps.loklak.org, I needed to add proper tools and libraries for smooth development of the World Mood Tracker app. In this section, I’ll be explaining the basic configuration that made it possible for a React app to be functional in the angular environment.

Pre-requisites

The most obvious prerequisite for the project was Node.js. I used node v8.0.0 while development of the app. Instead of npm, I decided to go with yarn because of offline caching and Internet speed issues in India.

Webpack and Babel

To begin with, I initiated yarn in the app directory inside project and added basic dependencies –

$ yarn init
$ yarn add webpack webpack-dev-server path
$ yarn add babel-loader babel-core babel-preset-es2015 babel-preset-react --dev

 

Next, I configured webpack to set an entry point and output path for the node project in webpack.config.js

module.exports = {
    entry: './js/index.js',
    output: {
        path: path.resolve('.'),
        filename: 'index_bundle.js'
    },
    ...
};

This would signal to look for ./js/index.js as an entry point while bundling. Similarly, I configured babel for es2015 and React presets –

{
  "presets":[
    "es2015", "react"
  ]
}

 

After this, I was in a state to define loaders for module in webpack.config.js. The loaders would check for /\.js$/ and /\.jsx$/ and assign them to babel-loader (with an exclusion of node_modules).

React

After configuring the basic presets and loaders, I added React to dependencies of the project –

$ yarn add react react-dom

 

The React related files needed to be in ./js/ directory so that the webpack can bundle it. I used the file to create a simple React app –

import React from 'react';
import ReactDOM from 'react-dom';

ReactDOM.render(
    <div>World Mood Tracker</div>,
    document.getElementById('app')
);

 

After this, I was in a stage where it was possible to use this app as a part of apps.loklak.org app. But to do this, I first needed to compile these files and bundle them so that the external app can use it.

Configuring the build target for webpack

In apps.loklak.org, we need to have a file by the name of index.html in the app’s root directory. Here, we also needed to place the bundled js properly so it could be included in index.html at app’s root.

HTML Webpack Plugin

Using html-webpack-plugin, I enabled auto building of project in the app’s root directory by using the following configuration in webpack.config.js

...
const HtmlWebpackPlugin = require('html-webpack-plugin');
const HtmlWebpackPluginConfig = new HtmlWebpackPlugin({
    template: './js/index.html',
    filename: 'index.html',
    inject: 'body'
});
module.exports = {
    ...
    plugins: [HtmlWebpackPluginConfig]
};

 

This would build index.html at app’s root that would be discoverable externally.

To enable bundling of the project using simple yarn build command, the following lines were added to package.json

{
  ..
  "scripts": {
    ..
    "build": "webpack -p"
  }
}

After a simple yarn build command, we can see the bundled js and html being created at the app root.

Using datamaps for visualization

Datamaps is a JS library which allows plotting of data on map using D3 as backend. It provides a simple interface for creating visualizations and comes with a handy npm installation –

$ yarn add datamaps

Map declaration and usage as state

A map from datamaps was used a state for React component which allowed fast rendering of changes in the map as the state of React component changes –

export default class WorldMap extends React.Component {
    constructor() {
        super();
        this.state = {
            map: null
        };
    render() {
        return (<div className={styles.container}>
                <div id="map-container"></div></div>)
    }
    componentDidMount() {
        this.setState({map: new Datamap({...})});
    }
    ...
}

 

The declaration of map goes in componentDidMount method because it would not be possible to start the map until we have the div with id=”map-container” in the DOM. It was necessary to draw the map only after the component has mounted otherwise it would fail due to no id=”map-container” in the DOM.

Defining data for countries

Data for every country had two components –

data = {
    positiveScore: someValue,
    negativeScore: someValue
}

 

This data is used to generate popup for the counties –

this.setState({
    map: new Datamap({
        ...
        geographyConfig: {
            ...
            popupTemplate: function (geo, data) {
                // Configure variables pScore so that it gives “No Data” when data.positiveScore is not set (similar for negative)
                return [
                    // Use pScore and nScore to generate results here
                    // geo.properties.name would give current country name
                ].join('');
            }
        }
    })
});

The result for countries with unknown data values look something like this –

Conclusion

In this blog post, I explained about introducing a React based app in app.loklak.org’s angular based environment. I discussed the setup and bundling process of the project so it becomes available from the project’s external HTTP server.

I also discussed using datamaps as a visualisation tool for data about Tweets. The app was first introduced in pull request fossasia/apps.loklak.org#189 and was improved step by step in subsequent patches.

Resources

Using Flask SocketIO Library in the Apk Generator of the Open Event Android App

Recently Flask SocketIO library was used in the apk generator of the Open Event Android App as it gave access to the low latency bi-directional communications between the client and the server side. The client side of the apk generator was written in Javascript which helped us to use a SocketIO official client library to establish a permanent connection to the server.

The main purpose of using the library was to display logs to the user when the app generation process goes on. This gives the user an additional help to check what is the mistake in the file uploaded by them in case an error occurs. Here the library established a connection between the server and the client so that during the app generation process the server would send real time logs to the client so that they can be viewed by the user displayed in the frontend.

To use this library we first need to download it using pip command:

pip install flask-socketio

This library depends on the asynchronous services which can be selected amongst the following listed below:

  1. Eventlet
  2. Gevent
  3. Flask development server based on Werkzeug

Amongst the three listed, eventlet is the best performant option as it has support for long polling and WebSocket transports.

The next thing was importing this library in the flask application i.e the apk generator of the app as follows:

from flask_socketio import SocketIO

current_app = create_app()
socketio = SocketIO(current_app)

if __name__ == '__main__':
    socketio.run(current_app)

The main use of the above statement (socket.run(current_app)) is that with this the startup of the web server is encapsulated. When the application is run in debug mode it is preferred to use the Werkzeug development server. However in production mode the use of eventlet web server or gevent web server is recommended.

We wanted to show the status messages currently shown to the user in the form of logs. For this firstly the generator.py file was looked upon which had the status messages and these were sent to the client side of the generator by establishing a connection between them using this library. The code written on the server side to send messages to the client side was as follows:

def handle_message(message):
    if message not None:
        namespace = “/” + self.identifier;
        send(message, namespace = namespace)

As we can see from the above code the message had to be sent to that particular namespace. The main idea of using namespace was that if there were more than one users using the generator at the same time, it would mean the send() method would send the messages to all the clients connected which would lead to the mixing up of status messages and hence it was important to use namespace so that a message was sent to that particular client.

Once the server sent the messages to the client we needed to add functionality to the our client side to receive the messages from them and also update the logs area with suitable content received. For that first the socket connection was established once the generate button was clicked which generated the identifier for us which had to be used as the namespace for that process.

socket = io.connect(location.protocol + "//" + location.host + "/" + identifier, {reconnection: false});

This piece of code established the connection of the socket and helps the client side to receive and send messages from and to the server end.

Next thing was receiving messages from the server. For this the following code snippet was added:

socket.on('message', function(message) {
    $buildLog.append(message);
});

This piece of code receives the messages from the server for unnamed events. Once the connection is established and the messages are received, the logs are updated with each message being appended so as to show the user the real time information about their build status of their app.

This was how the idea of logs being shown in the apk generator was incorporated by making the required changes in the server and client side code using the Flask SocketIO library.

Related Links:

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

Installation:

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”>
{{title}}
{{{title}}}
</script>

//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>
         </div>
         <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}}}">
                       </a>
                       {{{name}}}
                     </div>
                   </div>
                 {{/each}}
               {{/each}}
             </div> <!-- sponsor-row -->
           </div>
         </div>
       </section>
     </div>
   {{/if}}

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.