Master the JavaScript BasicsPermalink
Having a solid understanding of JavaScript fundamentals like scopes, hoisting, functions, closures, and data types will help immensely when learning React. Take some time to revisit JavaScript basics through resources like MDN’s JavaScript tutorial. Grasping core JavaScript concepts will allow you to pick up React concepts more easily without getting bogged down by syntax. JavaScript language fundamentals like variable scoping, hoisting, functions, and data types form the building blocks of any JavaScript application – including those built with React. Taking time to ensure you understand JavaScript fundamentals will pave the way for smoother React learning.
Leverage Array and Object MethodsPermalink
Arrays and objects are ubiquitous data structures in JavaScript and React. Familiarizing yourself with powerful methods like Array.map(), Array.filter(), and Object.keys() allows you to work with collections of data in a more functional style. Resources like JavaScript.info provide in-depth explanations of array and object methods that are important to understand before learning React.
Get Comfortable with FunctionsPermalink
Embracing functional programming principles like pure functions is critical for building applications the React way. Take some time to understand function declarations, expressions, parameters, return values, closures, and the importance of side-effect-free functions. Avoid mutating state wherever possible for optimal React development. References like “Mastering the JavaScript Interview” explain pure functions clearly.
Asynchronous JavaScript DemystifiedPermalink
Asynchronicity is a core concept in React applications which make heavy use of promises and asynchronous operations like AJAX requests. Make sure you have a firm grasp of asynchronous JavaScript with promises before touching React. Resources like “An Incremental Promises Tutorial” and posts on async/await provide clear introductions to taming asynchronous JavaScript.
Leverage Modern JavaScript FeaturesPermalink
ES2015 (ES6) introduced many features that made JavaScript more elegant and React’s syntax more palatable. Familiarize yourself with ES6 syntax like let/const, arrow functions, template literals, classes, and modules which are used pervasively in React codebases. Understanding modern JavaScript features enables you to read and write React code fluently.
Work with Data in the BrowserPermalink
Knowing how to retrieve, store, and modify data from client-side browser applications is invaluable for React development. Make sure you understand XMLHttpRequest, Fetch API, and common data exchange formats like JSON. A clear understanding of client-side data workflows prepares you to integrate RESTful APIs and back-end data sources with React.
Events and the DOMPermalink
Since React renders UI components to the DOM, having a solid mastery of DOM manipulation and event handling in JavaScript is critical. Thoroughly study how events are handled under-the-hood and basics of the DOM API. Assembling a complete understanding of the DOM lays the foundation for your React learning journey ahead. Spending time to solidify your JavaScript fundamentals in these core areas before taking the plunge into React will prevent a lot of frustration down the road. Focus on truly internalizing the key concepts – don’t just gloss over them. With the proper JavaScript prerequisites out of the way, you’ll be well positioned to get the most value from your React learning experience. 
