How do JavaScript-based modal/popup services like KissInsights and Hello Bar work?

Question

I'm developing a modal/popup system for my users to embed in their sites, along the lines of what KissInsights and Hello Bar (example here and here) do.

What is the best practice for architecting services like this? It looks like users embed a bit of JS but that code then inserts additional script tag.

I'm wondering how it communicates with the web service to get the user's content, etc.

TIA

Answer 1

You're right that usually it's simply a script that the customer embeds on their website. However, what comes after that is a bit more complicated matter.

1. Embed a script

The first step as said is to have a script on the target page.

Essentially this script is just a piece of JavaScript code. It's pretty similar to what you'd have on your own page.

This script should generate the content on the customer's page that you wish to display.

However, there are some things you need to take into account:

• You can't use any libraries (or if you do, be very careful what you use): These may conflict with what is already on the page, and break the customer's site. You don't want to do that.
• Never override anything, as overriding may break the customer's site: This includes event listeners, native object properties, whatever. For example, always use addEventListener or addEvent with events, because these allow you to have multiple listeners
• You can't trust any styles: All styles of HTML elements you create must be inlined, because the customer's website may have its own CSS styling for them.
• You can't add any CSS rules of your own: These may again break the customer's site.

These rules apply to any script or content you run directly on the customer site. If you create an iframe and display your content there, you can ignore these rules in any content that is inside the frame.

2. Process script on your server

Your embeddable script should usually be generated by a script on your server. This allows you to include logic such as choosing what to display based on parameters, or data from your application's database.

This can be written in any language you like.

Typically your script URL should include some kind of an identifier so that you know what to display. For example, you can use the ID to tell which customer's site it is or other things like that.

If your application requires users to log in, you can process this just like normal. The fact the server-side script is being called by the other website makes no difference.

Communication between the embedded script and your server or frames

There are a few tricks to this as well.

As you may know, XMLHttpRequest does not work across different domains, so you can't use that.

The simplest way to send data over from the other site would be to use an iframe and have the user submit a form inside the iframe (or run an XMLHttpRequest inside the frame, since the iframe's content resides on your own server so there is no cross domain communication)

If your embedded script displays content in an iframe dialog, you may need to be able to tell the script embedded on the customer site when to close the iframe. This can be achieved for example by using window.postMessage

For postMessage, see http://ejohn.org/blog/cross-window-messaging/

For cross-domain communication, see http://softwareas.com/cross-domain-communication-with-iframes