UI Engineer:

A front-end web developer is responsible for implementing visual elements that users see and interact with in a web application. Afront-end developer uses a combination of HTML, CSS, and JavaScript to build everything a user sees and interacts with on a website.The front-end developer creates the environment for everything that users see and touch: content, layout, and interaction. Your website is a sum of layers structure, data, design, content, and functionality. Creating that user-facing functionality is the job of a front-end developer. Using a combination of markup languages, design, and client-side script and frameworks.

What is a component?
For the sake of this article, we'll define component as an independent piece of software. This standalone, discrete piece of software has a clear boundary that is accessible via an API and contains all of the application dependencies. This enables teams to build the user interface quickly, leveraging the library of components.
A component-based UI Approach Accelerates Development
Using a component-based UI approach supports iterative, agile development. Components are hosted in a library from which teams can access, integrate and modify them throughout the development process.
An example of an application that uses UI components is Salesforce Lightning Design System. This is a collection of design patterns, components, and guidelines for creating a unified UI in the Salesforce ecosystem. This type of framework enables design governance and a streamlined experience.