Building interactive elements with HTML and javascript: Interact.js + resizing

{ Repost from my personal blog @ }

In a few of the past blog posts, we saw about implementing resizing with HTML and javascript. The functionality was pretty basic with simple resizing. In the last blog post we saw about interact.js.

interact.js is a lightweight, standalone JavaScript module for handling single-pointer and multi-touch drags and gestures with powerful features including inertia and snapping.

Getting started with Interact.js

You have multiple option to include the library in your project.

  • You can use bower to install (bower install interact) (or)
  • npm (npm install interact.js) (or)
  • You could directly include the library from a CDN (
Implementing resizing

Let’s create a simple box using HTML. We’ll add a class called resizable to it so that we can reference it to initialize Interact.js

<div class="resizable">  
    Use right/bottom edge to resize

We need to create an interact instance. Once the instance is created, we have to call the resizable method on it to add resize support to the div.

    edges: { right: true, bottom: true }
  .on('resizemove', function (event) {


Inside the resizable method, we can pass configuration options. The edgesconfig key allows us to specify on which all edges, resizing should be allowed. Right now, we have allowed on the right and bottom edges. Similarly we can have resizing support in the top and left edges too.

The resizemove event is triggered by interact every time the user tries to resize the div. From the event, we can get the box that is being resized, (i.e) the target by accessing

The event object also provides us event.rect.width and event.rect.height which is the width and height of the div after resizing. We’ll not set this as the width of the div so that, the user is able to see the width change.

var target =;
    // update the element's style  = event.rect.width + 'px'; = event.rect.height + 'px';

We can also instruct Interact.js to preserve the aspect ratio of the box by adding an option preserveAspectRatio: true to the configuration object passed to resizable method during initialization.

    edges: { right: true, bottom: true }
  .on('resizemove', function (event) {
    var target =;

    // update the element's style  = event.rect.width + 'px'; = event.rect.height + 'px';

Resizing and drag-drop (with Interact.js) were used to create the Scheduler tool at Open Event. The tool allows event/track organizers to easily arrange the sessions into their respective rooms by drag-drop and also to easily change the timings of the events by resizing the event block. The entire source code of the scheduler can be viewed at app/static/js/admin/event/scheduler.js in the Open Event Organizer server’s GitHub repository.


Update Fields with Array Input

Screenshot from 2016-07-15 17:57:58.png

There are certain fields in form where instead of a single value, we need an array of values to be stored. This are fields under the same category but having multiple elements, e.g., Tracks, Session Types, Microlocations, Sponsors, Social Links and similar such fields. Now as we know the way of doing this using simple html is provide the <input> tag with property “name” as “<field_name>[]”. So suppose we want to save the names of the mutliple tracks, we will have something like this
Screenshot from 2016-07-15 18:02:09.png

But the problem begins when you want to update name of a particular element (in this case Track). How to do it? Should we delete and create entries again? That doesn’t sound too good, does it? So what should we do? Let’s see….

Continue reading Update Fields with Array Input

Handling file uploading in HTML5 and Express

The Open Event Webapp Generator has a pure HTML front end form, and Express based backend.


We needed an option where users can upload their own JSON files to create a schedule page for it.

On the HTML form that’s easy. As you can see here we simple add input tags with type=”file”

<input type="file" name="sponsorfile" id="sponsorfile">

In our express app, we need to use multer to be able to handle file uploads.

We create a middleware called uploadedFiles, and pass the middleware to the get() block


var express = require('express');
var multer = require('multer');
var app = express();

var upload = multer({dest: 'uploads/'});

var uploadedFiles = upload.fields([
  {name: 'speakerfile', maxCount: 1},
  {name: 'sessionfile', maxCount: 1},
  {name: 'trackfile', maxCount: 1},
  {name: 'sponsorfile', maxCount: 1},
  {name: 'eventfile', maxCount: 1},
  {name: 'locationfile', maxCount: 1}
]);'/live', uploadedFiles, function(req, res) {
         // req.files has the files
         // req.body has the POST body params

Now we can access the files inside req.files (that will have a path to the temporary location of the file, you’ll have to use some filesystem module to read the files)

Transmitting response from a Web page to a server.

{ Re-post from my Medium Post }

My project has pivoted from a standalone android app to a Web page that will generate a custom app for an event organizer’s use.

Read up here on what my project actually is.

So obviously some changes at the server are to be made to make this possible.

How are you planning to do it?

First of we started by providing a Web page that the organizers can use to submit information about the app they need to be built like the App’s name, the link to the API (for fetching the json files) and their email address (for mailing them the apk once it’s generated).

The HTML file for the same can be found here.

Some changes to the Travis build should also be made so that it can use this data for building.

From there on, the details submitted by them will be converted by a json object (using javascript) and further send to the open event server via a POST request where it will be written to a database.

We will be able to fetch this file from the database by the following link

Simultaneously one Travis build will also be trigger using the API that will auto build the latest commit, taking the modified json file data provided by the orga-server.

This configuration will be provided to Travis while the build time.

Cool, any difficulties yet!

One of the main challenges that we are facing is manually triggering the Travis build.

We can do this via the Travis API but that’s still in beta and also we are getting our head around on how to implement it.

I also had a tough time learning javascript and HTML for making the Web page and then I also have to read up on sending a POST request to the server via Ajax.

It’s a bit tough, but should be fun.

So, that was all for now, see you next week and all the best for your projects.✌