How to convert Java apps to JavaScript with CheerpJ

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Sometimes, you need to convert your Java programming into JavaScript. In this article, Kayla Matthews explains how you can save time with the CheerjP tool to convert Java into JavaScript, just like that!

Many feel that JavaScript is superior to Java. For starters, it’s not aging like Java. But also, it’s much easier to understand and work with especially for weekend warriors. Of course, the two function very differently.

Java can stand on its own, while JavaScript must be placed inside an HTML document – sometimes referred to as a container.

JavaScript, HTML, and CSS are specifically designed for web applications and web development. Java, on the other hand, can be embedded into a full-blown proprietary application. It does not require anything else to function. These days, everything is making the jump to the web or some form of web applet for use on existing platforms, like mobile, for instance.

The differences make it difficult to convert aging Java apps and code to JavaScript. Often, it can be a long, drawn-out process requiring more than one programmer to complete the scope of the work.

CheerpJ—a new compiler technology—is about to change all that.


Cheerpj is a unique tool that will convert Java bytecodes into JavaScript, allowing developers to move their applications and software to the web with relative ease.

The best part is it doesn’t require a plugin or Java installation to work. For good measure, this means you don’t have to go through the trouble of downloading, installing, and configuring a Java environment and IDE.

It even has an offline compiler, to move Java to JavaScript with little to no effort. Server-side Java components can convert into client-side libraries for use in a browser. That’s a huge deal and will allow developers to take their standalone product, or app, to the web. Effectively, it could mean opening up your aging application or tool to more users, on more platforms and devices.

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Due to the nature of JavaScript, finished applets will be less rigid, easier to understand when reading the raw code and much more colorful in terms of interaction and events. JavaScript is often associated with web page events and actions regarding website development. Conventional Java isn’t exactly conducive to this sort of thing.

Plus, with JavaScript, you can be much more specific in your object and action calls. For instance, you can reference existing items like the status bar or browser window and make updates or changes directly to that component. You can’t do this with Java.

JavaScript is also compatabile with many leading technologies. For example, Widevine’s Encrypted Media Extentsions (also known as EME) relies on JavaScript to manage digital rights licenses across multiple devices and servers.

While tools like CheerpJ already exist – namely the Google Web Toolkit, which also allows you to put your Java content in a browser – Learning Technologies  says CheerpJ is remarkably different from other platforms, like Google’s.

What sets CheerpJ apart is that other platforms don’t offer full support for Java constructions and deployment. They only contain a partial implementation and reference to the Java runtime library.

So, developers will have a much easier time converting new and young applications to browsers, but existing apps with established code will be more difficult. Obviously, that’s not the case with this new compiler which means it opens up so many doors for the developers and founders of existing and long-standing Java applications.

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Of course, you could argue Java developers will need to familiarize themselves with JavaScript first if they aren’t already using it. While the languages and usage scenarios are similar, there are some differences that will make active development difficult if you don’t know what sets them apart.

Luckily, the jump from Java to JavaScript is a fairly easy and quick one to make as far as language shifts are concerned.

General availability

A limited release went live in July, but not everyone can get their hands on it just yet. A public release won’t be ready until later in November, which will be the official commercial version. If you’re not already a part of the limited access team, you’ll have to wait until after the public launch.

Still, it’s been a long time coming so a few months longer to wait is nothing, especially for Java developers that have been around since the early days.

It’s worth noting that an additional release will be available as a Chrome browser extension. The web applet will allow Java apps to be run without plugins or full environment installations.