Preview:
```// 1. push()
// Appends one or more elements to the end of an array
let arr1 = [1, 2, 3];
arr1.push(4);
console.log(arr1); // [1, 2, 3, 4]

// 2. pop()
// Removes the last element from the array and returns it
let arr2 = [1, 2, 3];
let lastElement = arr2.pop();
console.log(lastElement); // 3
console.log(arr2); // [1, 2]

// 3. shift()
// Removes the first element from the array and returns it
let arr3 = [1, 2, 3];
let firstElement = arr3.shift();
console.log(firstElement); // 1
console.log(arr3); // [2, 3]

// 4. unshift()
// Appends one or more elements to the beginning of an array
let arr4 = [2, 3];
arr4.unshift(1);
console.log(arr4); // [1, 2, 3]

// 5. concat()
// Combines two or more arrays
let arr51 = [1, 2];
let arr52 = [3, 4];
let newArr5 = arr51.concat(arr52);
console.log(newArr5); // [1, 2, 3, 4]

// 6. slice()
// Returns a new array containing part of the original array
let arr6 = [1, 2, 3, 4];
let newArr6 = arr6.slice(1, 3);
console.log(newArr6); // [2, 3]

// 7. splice()
// Changes the contents of an array by removing, replacing, or adding new elements
let arr7 = [1, 2, 3, 4];
arr7.splice(1, 2, 'a', 'b');
console.log(arr7); // [1, 'a', 'b', 4]

// 8. forEach()
// Executes the specified function once for each element of the array
let arr8 = [1, 2, 3];
arr8.forEach(element => console.log(element));
// 1
// 2
// 3

// 9. map()
// Creates a new array with the results of calling the specified function for each element of the array
let arr9 = [1, 2, 3];
let newArr9 = arr9.map(element => element * 2);
console.log(newArr9); // [2, 4, 6]

// 10. filter()
// Creates a new array with all elements that passed the test implemented by the given function
let arr10 = [1, 2, 3, 4];
let newArr10 = arr10.filter(element => element % 2 === 0);
console.log(newArr10); // [2, 4]

// 11. reduce()
// Applies a function to each element of an array (from left to right) to reduce it to a single value
let arr11 = [1, 2, 3, 4];
let sum = arr11.reduce((accumulator, currentValue) => accumulator + currentValue, 0);
console.log(sum); // 10

// 12. find()
// Returns the first element of the array that satisfies the given function
let arr12 = [1, 2, 3, 4];
let found = arr12.find(element => element > 2);
console.log(found); // 3

// 13. findIndex()
// Returns the index of the first array element that satisfies the given function
let arr13 = [1, 2, 3, 4];
let index = arr13.findIndex(element => element > 2);
console.log(index); // 2

// 14. some()
// Checks whether at least one element of the array satisfies the condition implemented by the function
let arr14 = [1, 2, 3, 4];
let hasEven = arr14.some(element => element % 2 === 0);
console.log(hasEven); // true

// 15. every()
// Checks whether all elements of an array satisfy the condition implemented by the function
let arr15 = [1, 2, 3, 4];
let allEven = arr15.every(element => element % 2 === 0);
console.log(allEven); // false

// 16. sort()
// Sorts the elements of an array and returns the sorted array
let arr16 = [3, 1, 4, 2];
arr16.sort();
console.log(arr16); // [1, 2, 3, 4]

// 17. reverse()
// Reverses the order of the elements in the array
let arr17 = [1, 2, 3, 4];
arr17.reverse();
console.log(arr17); // [4, 3, 2, 1]

// 18. join()
// Combines all elements of the array into a row
let arr18 = [1, 2, 3, 4];
let str = arr18.join('-');
console.log(str); // "1-2-3-4"

// 19. includes()
// Tests whether an array contains a specified element
let arr19 = [1, 2, 3, 4];
let hasThree = arr19.includes(3);
console.log(hasThree); // true

// 20. flat()
// Creates a new array with all subarray elements submerged to the specified depth
let arr20 = [1, [2, [3, [4]]]];
let flatArr = arr20.flat(2);
console.log(flatArr); // [1, 2, 3, [4]]

// 21. flatMap()
// First, it displays each element using a function, and then sums the result into a new array
let arr21 = [1, 2, 3];
let flatMappedArr = arr21.flatMap(element => [element, element * 2]);
console.log(flatMappedArr); // [1, 2, 2, 4, 3, 6]```