React

React is a framework for designing user interfaces with Javascript. Similar to other frameworks like Angular and Vue.js, React was designed by Facebook and released to the public as an Open Source project.  It helps organize development into a Model/View architecture that includes templated HTML and a structured way of handling input from the user.

If you are looking to design a Javascript based mobile app with the React framework, you may want to consider Ionic.

Advantages

The structure provided by an app framework helps keep your project organized from the beginning.  Often the overhead of integrating your code is made up by functionality and optimization done in the framework itself.  Especially with Javascript, there are numerous ways that event handlers and state changes can slip by each other and cause bugs.  A framework helps keep these issues from happening in the first place.

Risks

Large data changes can potentially cause large performance problems in frameworks that don't recalculate the DOM efficiently.  Careful organization of how your APIs serve data and how your app handles that data can keep things moving swiftly.