Cheatsheet

React Quick Reference

Intermediate React

• useState container for state within component (instance props). Use a store for data.

• useEffect Update render callback; update when something happens - async events. It's scheduled and you don't know when its going to run

• useContext globall application state (globals) and make it available specifically

• useRef container for state reference outside of the application scope (modals, subscriptions) aka static class properties exists across class instances. Referring to dom elements within react application

• useReducer similar to filter, pass in state run it through reducer and return state. Good for testing. Decoupling state from display layer 

• Redux good for managing global state. Use useState for inner-component state.

• Object.assign differential updating

• useMemo caching expensive computation preventing re-render only on change. For specific use cases. Have performance problems before using this

• useCallback implemented with useMemo. Takes in a function and a dependency, returns the same function so does not cause rerender.

• memo continue only when props change, for functional components

• useLayoutEffect similar to class component componentDidUpdate: happens immediately after your render finishes. Suitable for animation or measuring the dom

• useImperativeHandle very rare, useful for library authors. Exposes a function to the parent component.

• useDebugValue Add information readable by React Dev Tools in the DebugValueComponent. Console log for custom hook

• tailwind skipped

• redux : 

  • state tree. React sends actions and reads state from redux. 

  • useDispatch: query the storeh

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• test: 

  • test from the user perspective, button changed x to y

  • test features that are important to your app

  • test that fails on the bug, then make that test pass by fixing the bug.

  • No tests are better than bad tests (which take away confidence)

• Higher Order Component: reusable logic