JS Array

Question 1

Array.concat(array)

Answer 1

Combines both arrays and returns a new array without changing existing

Question 2

When do async tasks is it better to use a forEach method or a for loop?

Answer 2

The for loop is better. forEach() is synchronous.

Question 3

forEach()

Answer 3

synchronous method that will be used on all elements in an array

Question 4

every()

Answer 4

works on elements in an array until it returns a falsy value

Question 5

some()

Answer 5

loops through the array until the callback returns a truthy value

Question 6

filter()

Answer 6

creates a new array with the callback values that returned truthy

Question 7

map()

Answer 7

creates a new array from the values returned by the callback

Question 8

reduce()

reduceRight()

Answer 8

builds up a value by repeatedly using the callback

reduceRight is in descending order RTL

needs an accumulator ‘sum’ | ‘total’

const total = numbers.reduce((sum, value) => {
  return sum + value;
})

Question 9

push() and pop()

Answer 9

used to add to the tail and remove elements from the tail of an array

Question 10

How is performance for forEach() or reduce() versus a traditional for loop?

Answer 10

forEach() and reduce() are faster for small to medium datasets, for loop is faster for large datasets (500,000+)

Question 11

.from()

Answer 11

creates and array from a string

Array.from(“string”)

Question 12

.toString()

Answer 12

returns a string with the array values seperated by commas

Question 13

shift() and unshift()

Answer 13

Shift dequeues and element from the head

unshift inserts an element at the head

Question 14

.sort() and .reverse()

Answer 14

sorts and reverses an array

Question 15

.slice()

Answer 15

returns selected elements of an array as a new array(inclusive, exclusive)

Question 16

.splice()

Answer 16

adds or removes items from an array

Array.splice(index, quantityToRemove, insert1, insert2,…)

Question 17

includes()

Answer 17

returns true if an array contains the value

Question 18

length

Answer 18

returns the size of the array

Question 19

How can you instantiate an array of fixed size?

Answer 19

array = new Array(size);

Question 20

Array.from()

Answer 20

Creates a new Array instance from an array-like object or iterable object.

Question 21

Array.isArray()

Answer 21

Returns true if the argument is an array, or false otherwise.

Question 22

Array.of()

Answer 22

The Array.of() method creates a new Array instance from a variable number of arguments, regardless of number or type of the arguments.

Array.of(7); // [7] 1 slot
Array(7); // array of 7 empty slots

Question 23

Array.at()

Answer 23

Returns the array item at the given index. Accepts negative integers, which count back from the last item.

Question 24

Array.prototype.find()

Answer 24

Returns the value of the first element in the array that satisfies the provided testing function, orundefinedif no appropriate element is found.

Question 25

Array.prototype.findLast()

Answer 25

Returns the value of the last element in the array that satisfies the provided testing function, or undefined if no appropriate element is found.

Question 26

Array.prototype.findIndex() | Array.prototype.findLastIndex()

Answer 26

Returns the index of the first element in the array that satisfies the provided testing function, or -1 if no appropriate element was found. Returns the index of the last element in the array that satisfies the provided testing function, or -1 if no appropriate element was found.

Question 27

Array.fill()

Answer 27

Fills all the elements of an array from a start index to an end index with a static value.

Question 28

Array.prototype.join()

Answer 28

Joins all elements of an array into a string.

Question 29

Array.prototype.keys()

Answer 29

Returns a new array iterator that contains the keys for each index in the calling array.

Question 30

Array.toLocaleString()

Answer 30

Returns a localized string representing the calling array and its elements. Overrides the Object.prototype.toLocaleString() method.

Question 31

Array.prototype.indexOf() Array.prototype.lastIndexOf()

Answer 31

Returns the first (least) index at which a given element can be found in the calling array. Returns the last (greatest) index at which a given element can be found in the calling array, or -1 if none is found.

Question 32

Array.prototype.values()

Answer 32

Returns a new array iterator object that contains the values for each index in the array.

Question 33

Array.prototype.copyWithin()

Answer 33

Copies a sequence of array elements within an array.

Question 34

Array.prototype.flat()

Answer 34

Returns a new array with all sub-array elements concatenated into it recursively up to the specified depth.

Question 35

Array.prototype.flatMap()

Answer 35

Returns a new array formed by applying a given callback function to each element of the calling array, and then flattening the result by one level.