React TL;DR Recap. The Most Useful React Content From 2019


All React + TypeScript Cheatsheets

  • The Basic Cheatsheet (/ is focused on helping React devs just start using TS in React apps
  • The Advanced Cheatsheet (/ helps show and explain advanced usage of generic types for people writing reusable type utilities/functions/render prop/higher ordercomponents and TS+React libraries.
  • The Migrating Cheatsheet (/ helps collate advice for incrementally migrating large codebases from JS or Flow, from people who have done it.
  • The HOC Cheatsheet (/ specifically teaches people to write HOCs with examples.

5 Tips to Help You Avoid React Hooks Pitfalls

  • Read React Hooks documentation and FAQ before you start.
  • Install, use, and follow the ESLint plugin.
  • Don’t think about Lifecycles, think about synchronizing side effects to state.
  • Know that React is fast by default and do some digging before applying performance optimizations pre-maturely.
  • Avoid testing implementation details.

Introducing Concurrent Mode (Experimental)

Concurrent Mode is a set of new features (still experimental!) that help React apps stay responsive and adjust to the user’s device capabilities and network speed.


  • Suspense for Data Fetching – describes a new mechanism for fetching data in React components.
  • Concurrent UI Patterns – shows some UI patterns made possible by Concurrent Mode and Suspense.
  • Adopting Concurrent Mode – explains how you can try Concurrent Mode in your project.
  • Concurrent Mode API Reference – documents the new APIs available in experimental builds.

Announcing React Native 0.61 with Fast Refresh

Fast Refresh:

  • fully supports modern React, including function components and Hooks.
  • recovers after typos and other mistakes, and falls back to a full reload when needed.
  • doesn’t perform invasive code transformations so it’s reliable enough to be on by default.

Other Improvements and changes:

  • Fixed use_frameworks! CocoaPods support.
  • Add useWindowDimensions Hook – This new Hook automatically provides and subscribes to dimension updates, and can be used instead of the Dimensions API in most cases.
  • Remove React .xcodeproj.

Functional Programming in JavaScript: How and Why?

Functional Programming is a programming paradigm where you mostly construct and structure your code using functions.


  • First-class citizens functions: you can always insert functions inside a function without any restrictions present.
  • A higher-order function: a function that gets a function as an argument.
  • Function Composition: an act of composing/creating functions that allow you to further simplify and compress your functions by taking functions as an argument and return an output.


  • It doesn’t have side-effects and it’s immutable
  • It’s clean, straightforward and KISS

Test Driven Development (TDD) with React, React Testing Library, and Jest

A strategy for writing a good test:

  • Write a test that fails (RED). This is to avoid false positives (tests passing when they shouldn’t be)
  • Write the minimum amount of code required to get the test passing (GREEN).
  • Refactor the code (REFACTOR). This might mean writing a more efficient technical solution or a more refined approach. As long as the test continues to stay green, you know there is no regression.

Announcing TypeScript 3.7

TypeScript 3.7 arrived with a lot of great features 🎉🎉🎉


  • Optional Chaining
  • Nullish Coalescing
  • Assertion Functions
  • Better Support for never-Returning Functions
  • –declaration and –allowJs
  • (More) Recursive Type Aliases
  • The useDefineForClassFields Flag and The declare Property Modifier
  • Build-Free Editing with Project References
  • Uncalled Function Checks
  • Flatter Error Reporting
  • // @ts-nocheck in TypeScript Files
  • Semicolon Formatter Option
  • Website and Playground Updates

Breaking Changes:

  • DOM Changes
  • Class Field Mitigations
  • Function Truthy Checks
  • Local and Imported Type Declarations Now Conflict
  • API Change

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