FE Interview Cheat Sheet

A Programming › JavaScript cheat sheet in English by Dison

Frontend interview quick reference lookup

4,338 views 584 downloads 6 Feb 2022 History

PRs

React Setup

Add Script	<script src="foo.com/react.js" crossorigin />
Add targeting div	<div id="react" />
Get root Dom	root = document.getElementById("root");
Bootstrap React	ReactDOM.render(<App />, rootElement);

React Hooks

const [state, setState] = useState(initialState);

useEffect(() => { ...logic, return cleanup}, [deps]);

useMemo(() => computeExpensiveValue(a, b), [a, b]);

Context
   ThemeContext = React.createContext(themes.light);
   <ThemeContext.Provider value={themes.dark}>

   theme = useContext(ThemeContext);
   background: theme.background

useRef
   const inputEl = useRef(null);
   <input ref={inputEl} />
   inputEl.current.focus();

async useEffect

useFetch = (param) => {
  const [state, setState] = useState([]);  

  useEffect(() => {
    async function fetchData() {      
      const response = await fetch('url');      
      const data = await response.json();

      setState((prev) => prev.concat(data.results));      
    }
    fetchData();
  }, [param]);

  return { state };
};

JS Arrays

Insert at Start	unshift()
Insert at End	push()
Insert at Location	splice(start, 0, item2, itemN)
Remove First	shift()
Remove Last	pop()
Remove at Location	splice(start, deleteCount)
Get parts	slice(start, end)

Algos

DFS	getNodes(root) [...getNodes(root.left), getNodes(root.right)]
BFS	while(queue.length) for(queue.length) node = queue.shift() queue.push(node.left/right)

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