ES2016 brings with it Array.prototype.includes, ES2017 has async and await, ES2018 adds new capabilities to regular expressions and async iterators, ES2019 has Object.fromEntries, Array.prototype.flat and flatMap, and ES2020 has dynamic imports, globalThis, and BigInt.
Refactor es5 functions to es6 arrow functions
Explore ES2019 stable array sorting by example
Use ES2019 Array.prototype.flat to Flatten Multidimensional Arrays
Map and Flatten Multidimensional Arrays with ES2019 Array.prototype.flatMap