Javascript

Javascript is at the heart of almost every site on the internet.  It allows developers to provide nearly the same functionality available in desktop applications on websites.  These "Web Applications" are becoming more and more common, even replacing mobile applications in some cases.  Thanks to runtime environments like NodeJS and mobile app frameworks like Cordova, Javascript can be run on anything from servers to smartphones.

Advantages

The work done with Javascript can be reused across multiple platforms to ensure compatibility and save time. Node.js allows you to run an API or server-side service with the same code used client-side. Browsers all have Javascript support built right in, and you can use Cordova to deploy that code on Apple and Android phones inside an App.

Modern Javascript frameworks like Vue and React give you a well structured way to make responsive and very functional end user interfaces that work well on webpages and mobile devices.  In most cases you can take that code straight from the web onto mobile devices in an app.  These frameworks give you powerful methods for updating the UI in real time based on event-based data changes coming in from hardware or web based APIs.

Risks

Like PHP, Javascript has relatively loose syntax rules that means developers can quickly write code, but sacrifice long term maintainability. This means it’s important to write clean code that is easily read and meets standards like Clean Code or pass quality test suites like JSLint.  This is one of the reasons using a framework is so important for even medium sized projects.

Javascript is also slower than compiled languages like Java. If your project needs to process large amounts of data, it may be necessarily to build backend utilities in other languages like Python.