How to write a function that returns a Promise resolving after one second?
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What happens if the component type changes? Will the same key help preserve the state?
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What is the difference between rendering and drawing? What is the process called that compares the virtual and real DOM trees?
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const SomeElement = ({ hasData }) => { if (hasData) { return <div> <DataElement /> <SomeImportantElement /> </div> } return <div> <SomeImportantElement /> </div> }
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// The findUnique method is applied to the array, which returns a new array of unique elements, // i.e., those that appear only once in the original array, in the same order. // Implement the findUnique method so that it works like a regular array method [10, 5, 10, 1, 6, 6, 7, 9, 9, 10].findUnique(); // [5, 1, 7]
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What is a closure in JavaScript? Where is it used in practice?
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What will happen if the dependencies array is not specified in useEffect? If you add count to the dependencies array and press the button, will the cleanup function be triggered?
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Apart from methods and key types, what else does Map have that objects do not?
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import React, { useState, useEffect, useRef, useContext, useReducer, useMemo, me const someFunc = (arr) => { return [...arr].sort((a, b) => a - b); }; const LazyInit = (props) => { const [arr, setArr] = useState(someFunc(props.arr)); const onClick = () => { setArr((prev) => prev.concat(prev.length + 1)) } return ( <> <button onClick={onClick}> Increment </button> <ul> {arr.map((n, index) => <li key={index}>{n}</li>)} </ul> </> ) } export default () => <LazyInit arr={[1, 2, 3]} />;
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Provide an example of a closure. Have you used closures in React?
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Explain what the Event Loop is. What belongs to microtasks and macrotasks?
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What is the purpose of the 'unknown' type in TypeScript? How can the type be narrowed?
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const doSomething = (ms) => { return new Promise((resolve, reject) => { setTimeout(() => { if (Math.random() <= 0.5) { reject("error"); } else { resolve(ms); } }, ms); }); }; const getDelay = () => { let rand = 1000 + Math.random() * 2000; return Math.floor(rand); }; const p1 = doSomething(getDelay()); const p2 = doSomething(getDelay()); const p3 = doSomething(getDelay()); const p4 = doSomething(getDelay());
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const a = {} a[1] = 'test' for ( ... )
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Tell about collections Map and Set in JavaScript — what do you know about them?
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What is the difference between sessionStorage and localStorage?
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What is the difference between the 'any' and 'unknown' types in TypeScript?
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What are the scopes of let/const and var? Is there another way to declare variables besides var, let, const?
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setTimeout(() => { console.log("timeOut"); }, 0) console.log(1); new Promise(resolve => { console.log("Promise"); setTimeout(() => { console.log("777"); resolve() }, 0) }).then(() => { console.log("then1"); }) .then(console.log('tratata')) .then(() => console.log("then2"); }) console.log(4); setTimeout(() => { console.log("timeOut2"); }, 0)
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const func = obj.sayHi() const boundFuns = func.bind(obj) boundFuns() ------------------- const submit = (el) => () => { log(el); } arr.map(el => <button onClick={submit(el)}/>) const param = useMemo(() => a + b) return <Child value={param} />
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