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const target1 = document; // correct

const target2 = document.body; // correct

const target3 = document.getElementById('blockId'); // correct

const target4 = window; // wrong

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MutationRecord = {
  addedNodes : [], // NodeList
  attributeName : null, // attribute name - string or null
  attributeNamespace : null, // attribute namespace
  nextSibling : null, // next sibling in DOM
  oldValue : null, // old value
  previousSibling : null, // previous sibling in DOM
  removedNodes : [], // NodeList of removed nodes
  target : Element, // target element
  type : "childList" // mutation type one of childList, attributes or characterData

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// target element that we will observe
const target = document.querySelector('div');

// config object
const config = {
  characterData: true,
  characterDataOldValue: true,
  childList: true,
  subtree: true
};

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// stop observing
observer.disconnect();

// empties observer instance and returns records 
observer.takeRecords(); // -> MutationRecords

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const users = [
  { 'user': 'barney',  'age': 36, 'active': true },
  { 'user': 'fred',    'age': 40, 'active': false },
  { 'user': 'pebbles', 'age': 1,  'active': true }
];

const timerDateFindLodash = new Date();
console.log('lodash find', find(users, ({ age }) => age < 40));
console.log('lodash time', new Date() - timerDateFindLodash);

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const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

const timerDateReduceLodash = new Date();
console.log('lodash reduce', reduce(numbers, (sum, n) => sum + n, 0));
console.log('lodash time', new Date() - timerDateReduceLodash);

const timerDateReduceJS = new Date();
console.log('native reduce', numbers.reduce((sum, n) => sum + n, 0));
console.log('native time', new Date() - timerDateReduceJS);

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/**
 * Main function
 */
function find(collection, predicate, fromIndex) {
  let iteratee
  const iterable = Object(collection)

  if (!isArrayLike(collection)) {
    collection = keys(collection)
    iteratee = (key) => predicate(iterable[key], key, iterable)

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reduce(map(filter(users, ({ active }) => active), ({ age }) => (age + 100) % 27), (p, c) => c > 20 ? p.concat(c) : p, []);

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users
  .filter(({ active }) => active)
  .map(({ age }) => (age + 100) % 27)
  .reduce((p, c) => c > 20 ? p.concat(c) : p, []);

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import * as React from 'react';

class Swiper extends React.PureComponent {
  startPointX = 0;
  startPointY = 0;
  direction = null;
  clicked = false;

  onMoveStart = ({ event, x, y }) => {
    const { onMoveStart } = this.props;