AND questions

`Array.prototype.sort` sorts the elements of an array in place and returns the sorted array. The sorting is based on the UTF-16 code units of the elements by default, but can be customized with a comparison function. 

const arr = [3, 1, 2];
arr.sort();
console.log(arr); // [1, 2, 3]

`Array.prototype.copyWithin` shallow copies a portion of the array to another location within the same array. It modifies the original array and returns the modified array. 

const arr = [1, 2, 3, 4];
arr.copyWithin(0, 2, 4);
console.log(arr); // [3, 4, 3, 4]

`Array.prototype.sort` sorts the elements of an array in place and returns the sorted array. By default, it sorts elements as strings. A custom comparator function can be provided to sort elements in other ways. 

const arr = [3, 1, 2];
arr.sort();
console.log(arr); // [1, 2, 3]

`String.prototype.localeCompare` compares two strings in the current locale and returns a number indicating whether the calling string comes before, after, or is equal to the compared string. 

const str1 = 'apple';
const str2 = 'banana';
const result = str1.localeCompare(str2);
console.log(result); // -1 (str1 is less than str2)

`String.prototype.includes` checks if a string contains a specified substring. It returns `true` if the substring is found, otherwise `false`. 

const str = 'hello';
console.log(str.includes('ell')); // true
console.log(str.includes('world')); // false

`String.prototype.substr` extracts a substring from a string based on a starting index and length. It returns the extracted substring. 

const str = 'hello world';
const substr = str.substr(6, 5);
console.log(substr); // 'world'

`String.prototype.slice` extracts a section of a string and returns it as a new string, without modifying the original string. 

const str = 'hello';
const sliced = str.slice(1, 4);
console.log(sliced); // 'ell'

`String.prototype.endsWith` checks if a string ends with a specified substring and returns `true` if it does, otherwise `false`. 

const str = 'hello';
console.log(str.endsWith('lo')); // true
console.log(str.endsWith('he')); // false

`Array.prototype.shift` removes the first element from an array and returns that element. It modifies the original array and shifts all subsequent elements down by one. 

const arr = [1, 2, 3];
const first = arr.shift();
console.log(first); // 1
console.log(arr); // [2, 3]

`Array.prototype.splice` changes the contents of an array by removing or replacing existing elements and/or adding new elements in place. It modifies the original array and returns an array containing the removed elements. 

const arr = [1, 2, 3, 4];
const removed = arr.splice(1, 2, 'a', 'b');
console.log(arr); // [1, 'a', 'b', 4]
console.log(removed); // [2, 3]

`Array.prototype.sort` sorts the elements of an array in place and returns the sorted array. By default, elements are sorted as strings. A custom sorting function can be used to specify the sort order. 

const arr = [3, 1, 2];
arr.sort((a, b) => a - b);
console.log(arr); // [1, 2, 3]

`String.prototype.startsWith` checks if a string starts with a specified substring and returns `true` if it does, otherwise `false`. 

const str = 'hello';
console.log(str.startsWith('he')); // true
console.log(str.startsWith('lo')); // false

`String.prototype.search` searches a string for a match against a regular expression and returns the index of the first match. If no match is found, it returns -1. 

const str = 'hello 123'; 
const index = str.search(/\d+/); 
console.log(index); // 6 

`Array.prototype.sort` sorts the elements of an array in place and returns the sorted array. By default, the elements are sorted as strings. A custom sorting function can be provided for different sorting logic. 

const arr = [3, 1, 2];
arr.sort();
console.log(arr); // [1, 2, 3]

`Array.prototype.unshift` adds one or more elements to the beginning of an array and returns the new length of the array. It modifies the original array. 

const arr = [2, 3];
arr.unshift(1);
console.log(arr); // [1, 2, 3]

`Array.prototype.reverse` reverses the elements of an array in place and returns the reversed array. It modifies the original array. 

const arr = [1, 2, 3];
arr.reverse();
console.log(arr); // [3, 2, 1]

`Array.prototype.splice` changes the contents of an array by removing or replacing existing elements and/or adding new elements in place. It modifies the original array and returns an array containing the removed elements. 

const arr = [1, 2, 3, 4];
const removed = arr.splice(2, 1, 'a', 'b');
console.log(arr); // [1, 2, 'a', 'b', 4]
console.log(removed); // [3]

`Array.prototype.toLocaleString` returns a string representing the array and its elements, formatted according to the locale and options. It uses the `toLocaleString` method of each element. 

const arr = [1, 2, 3];
console.log(arr.toLocaleString()); // '1,2,3' (may vary depending on locale)

`Array.prototype.pop` removes the last element from an array and returns that element. It modifies the original array. 

const arr = [1, 2, 3];
const last = arr.pop();
console.log(last); // 3
console.log(arr); // [1, 2]

`Array.prototype.flatMap` maps each element using a provided mapping function and then flattens the resulting array into a new array. It combines the map and flat operations into a single method. 

const arr = [1, 2, 3];
const flatMapArr = arr.flatMap(x => [x, x * 2]);
console.log(flatMapArr); // [1, 2, 2, 4, 3, 6]

React's Concurrent Mode introduces new rendering capabilities that allow React to interrupt and prioritize rendering work, improving user experience by making updates more responsive. It enables features like Suspense and useTransition, leading to smoother and faster UIs.

Techniques for managing side effects in React include using the useEffect hook for handling async operations, leveraging custom hooks to encapsulate side effect logic, and using libraries like Redux Thunk or Redux Saga for complex side effects management.

useImperativeHandle is a hook used to customize the instance value exposed when using refs. It's useful for controlling what methods or properties are exposed to parent components, such as managing focus or triggering animations from parent components.

React Suspense has limitations, including limited support for data fetching and potential performance issues with large components. These can be addressed by using concurrent features like useTransition, combining Suspense with other data fetching libraries, and adopting best practices for component design.

React StrictMode is a development tool that helps identify potential problems in an application by activating additional checks and warnings. It helps catch issues like deprecated APIs, unexpected side effects, and potential problems with components.