JavaScript Array Methods

Question 1

length

Answer 1

gives the length of an array

Question 2

pop( )

Answer 2

removes the last element

Question 3

push(el)

Answer 3

add an element to the end

Question 4

shift( )

Answer 4

Remove an element from the beginning

Question 5

unshift(el)

Answer 5

adds an element to the beginning

Question 6

join(“”)

Answer 6

Creates a string out of an array

Question 7

toString()

Answer 7

Creates a string out of an array

Question 8

.concat([])

Answer 8

Creates one array out of two

Question 9

slice(begin, end, step)

Answer 9

Returns the sliced part but does NOT mutate the original array.

Question 10

splice(start, amount, element, …)

Answer 10

mutates the original array by adding or removing elements.

Question 11

sort((a, b) => a - b)

Answer 11

sorts an array in ascending or descending order.

Question 12

delete arr[idx]

Answer 12

removes an element from an array.

Question 13

.indexOf(element, start )

Answer 13

finds the index of the first element matching the one given to the method. start is optional and determines where should the search begin. Returns -1 if it doesn’t find the element.

Question 14

.find(element )

Answer 14

returns the first element that satisfies the provided testing function otherwise returns undefined.

Question 15

includes( )

Answer 15

determines whether an array includes a certain value among its entries, returning true or false as appropriate.

Question 16

.at( integer )

Answer 16

takes an integer and return the item at that index, allowing for positive and negative integers.

Question 17

.entries( )

Answer 17

returns an array that contains key/value pairs for each index in the array

Question 18

.every(function, hisArg:optional)

Answer 18

checks if all the elements in the array pass the test. Returns a Boolean. if all pass the test returns true.

Question 19

.some(function, hisArg:optional)

Answer 19

Checks if one element in the array passes the test. If one passes then returns true. Otherwise, returns false.

Question 20

.filter(function, thisArg:optional)

Answer 20

creates a shallow copy of the elements in the array that pass the test.

Question 21

findIndex(function, thisArg: Optional)

Answer 21

Returns the first index of element in an array that satisfies the testing function, returns -1 if nothing passes the test.

Question 22

flat(depth:optional)

Answer 22

Creates a new array with all subarrays concatenated.

Question 23

flatMap(function, thisArg:optional)

Answer 23

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

Question 24

forEach(function, thisArg: optional)

Answer 24

Runs a function for each element in the array.

Question 25

Array.from()

Answer 25

creates a new, shallow copy instance from an iterable or array-like object.

Question 26

.keys()

Answer 26

returns an array iterator object that contains the keys for each index.

Question 27

map(function, thisArg: optional)

Answer 27

creates a new array populated with the results of calling a provided function on every element in the calling array.

Question 28

.reduce((acc, curr, idx)

Answer 28

instances executes a user-supplied “reducer” callback function on each element of the array, in order, passing in the return value from the calculation on the preceding element. The final result of running the reducer across all elements of the array is a single value.

Question 29

reverse()

Answer 29

reverses the whole array