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/**
 * Get user by id.
 * @param {number} id – Id of user
 * @return {User} Returns User.
 */
function getUserById(id) {
  //TO DO: implement it
}

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/**
 User definition
 @typedef {Object} User
 @property {number} id - Id of the user.
 @property {string} name - Name of the user.
 @property {string=} profession - Profession of the user. Is is optional.
 @property {function(string):string} setProfession - Set profession of user
 */

/** @type {User} */

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/** @typedef {{x:number, y:number}} Point */

/** @type {Point} */
var point;

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/** @type {(string|Array)} */
var address;

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/** @type {number} */
var price;

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const street;
if (user && user.address && user.address.street) {
	street = user.address.street;
}

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const street = ((user || {}).address || {}).street

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const street = user?.street?.address

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import { useState, useEffect } from 'react';

const useFetch = (request, payload) => {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);

  useEffect(() => {
    let isMounted = true;
    setError(null);

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import React from 'react'
import Emitter from '../services/emitter';

import '../styles/Header.css';

class Header extends React.Component {
    state = { header: 'Default header' };

    componentDidMount() {
        Emitter.once('INPUT_FROM_MAIN', (newValue) => this.setState({ header: newValue }));