Handson experience working with Object Oriented JavaScript (OOJS), JavaScript and practical uses in building complex interactive experiences, primarily with ECMAScript 2015+. You should be uptodate with new specifications (different stages), and also, using transpilers like Babel to use features from all stages
Good understanding of creational and structural design patterns in JavaScript
Experience working with Single Page Applications (SPA) with universal rendering capabilities.
Good understanding of React.js, its core principles lifecycle methods, React Hooks,virtual DOM etc. and at least 6 12 months handson experience with the same
Understanding of oneway data flow and the FluxRedux architecture.