Frontend

Kuidas sa mõistad, mis on render Reactis? Miks see võib juhtuda?

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import React, { useState, useEffect, useRef, useContext, useReducer, useMemo } from 'react'; export default Effects = () => { const [count, setCount] = useState(0); useLayoutEffect(() => console.log("katrs renderings 1")); console.log("katrs renderings 2"); useEffect(() => console.log("katrs renderings 3")); return ( <> <button onClick={() => setCount((prevProps) => ++prevProps)}> Palielināt </button> </> ) }

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Kas teil on kunagi olnud kogemust töötada ilma analüütikuta, kui pidite ülesannet ise mõistma?

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Mis on WeakMap?

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Millised seaded on küpsistel (httpOnly, secure, expires, domain, path)?

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const obj = [{ value: 1, elems: [ { value: 2, elems: [ { value: 3 }, { value: 6 }, ... ] }, { value: 4, elems: [ { value: 5, elems: [ { value: 6 }, ... ]} ] } ] }] ------------- setTimeout(() => { console.log(1); }, 0); const p = new Promise(resolve => { console.log(2); resolve(); }); p.then(() => { console.log(3) }).then(() => { console.log(4); }); console.log(5);

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const createCounter = () => {

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const { foo: bar, bar: foo } = { foo: 1, bar: 2 } console.log(bar) // console.log(foo) //

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Kuidas React võrdleb props'e? Kuidas töötab pinnalõike võrdlus?

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Räägi mulle Event Loopist: kuidas see töötab, mis on mikro- ja makroülesanded?

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const { foo: bar, bar: foo } = { foo: 1, bar: 2 }; //foo //bar setTimeout(() => { console.log("timeOut"); }, 0); console.log(1); new Promise((resolve) => { console.log("Promise"); setTimeout(() => { console.log("timeOut2"); resolve(); }, 0); }) .then(() => { console.log("then1"); }) .then(() => { console.log("then2"); }); console.log(4); setTimeout(() => { console.log("timeOut3"); }, 0);

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IT One

Milleks on useRef? Millised on selle kasutusvaldkonnad?

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const Effects = () => { const [count, setCount] = useState(0); useLayoutEffect(() => console.log("iga render 1")); console.log("iga render 2"); useEffect(() => console.log("iga render 3")); return ( <> {count} <button onClick={() => setCount((prevProps) => ++prevProps)}> Suurenda </button> </> ); }; export default Effects; // 1 render: // Pärast klõpsamist: const Effects = () => { const [count, setCount] = useState(0); const [number, setNumber] = useState(0); useEffect(() => { console.log(count); return () => { console.log(count); }; }); return ( <> {count} <button onClick={() => setCount((prevProps) => ++prevProps)}> Suurenda </button> </> ); }; export default Effects; // 1 render: // 2 1 3 // Pärast klõpsamist: // 2 1 3 // null: // 2 1 3 // // 1: 1, 0 // +: 1, 2 // ++: 2, 2

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import { useState, useRef, useEffect } from "react"; const useDebugRender = ({props}) => { const prevProp = useRef(props) useEffect(() => { }, []) } const ParentComponent = () => { const [random, setRandom] = useState(0); // Prop kaudu antakse lapsekomponendile const [text, setText] = useState(""); // Prop kaudu antakse lapsekomponendile const createRandom = () => setRandom(Math.floor(Math.random() * 100)); const onTextChange = (e) => setText(e.target.value); const [count, setCount] = useState(0); const incrementCount = () => setCount((prev) => prev + 1); // See funktsioon antakse Prop kaudu lapsekomponendile return ( <> <Count: {count} /> <input type="text" onChange={onTextChange} /> <button onClick={createRandom}>Genereeri juhuslik</button> <div> <ChildComponent random={random} text={text} incrementCount={incrementCount} /> </div> </> ); }; export default ParentComponent;

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Tüübi getParam nii, et TypeScript ise automaatselt esile tõstab objekti omadused. Tee tüübi määramine selliseks, et ei oleks võimalik edastada massiive.

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Miks kasutada debounce'i, mitte throttle'i otsingul?

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let obj = { a: 1 }; let array = [obj]; obj = null; console.log(obj); // console.log(array); //

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Kui vanemkomponent edastab uue massiivi propsina, kas näed ekraanil uusi andmeid või vanu? Miks?

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const submit = useCallback((el) => () => { log(el); }, []); arr.map(el => <button onClick={submit(el)} />) arr.map(el => <SomeComp key={} onClick={() => submit(el)} />) const param = useMemo(() => ({c: a + b}), [a,b]) return <Child value={param} /> Child = React.memo(() => {})

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Mis vahe on await p1, await p2 ja Promise.all([p1, p2]) vahel?

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