https://medium.com/siliconwat/data-structures-in-javascript-1b9aed0ea17c

As business logic moves from the back to the front more and more, expertise in Frontend Engineering becomes ever more crucial. As Frontend Engineers, we depend on view libraries like React to be productive. View libraries in turn depend on state libraries like Redux to manage the data. Together, React and Redux subscribe to the reactive programming paradigm in which UI updates react to data changes. Increasingly, backends act simply as API servers, providing endpoints only to retrieve and update the data. In effect, the backend just “forwards” the database to the frontend, expecting the Frontend Engineer to handle all the controller logic. The rising popularity of microservices and GraphQL attest to this growing trend.

Now, in addition to having aesthetic understanding of HTML and CSS, Frontend Engineers are expected to master JavaScript as well. As datastores on the client become “replicas” of databases on the server, intimate knowledge of idiomatic data structures is pivotal. In fact, an engineer’s level of experience can be inferred from his or her ability to distinguish when and why to use a particular data structure.