Array Methods

Question 1

.at()

Answer 1

The at() method takes an integer value and returns the item at that index, allowing for positive and negative integers. Negative integers count back from the last item in the array

Question 2

.concat()

Answer 2

The concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.

Question 3

.copyWithin

Answer 3

The copyWithin() method shallow copies part of an array to another location in the same array and returns it without modifying its length.

Question 4

.entries()

Answer 4

The entries() method returns a new Array Iterator object that contains the key/value pairs for each index in the array.

Question 5

.every()

Answer 5

The every() method tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value.

Question 6

.fill()

Answer 6

The fill() method changes all elements in an array to a static value, from a start index (default 0) to an end index (default array.length). It returns the modified array.

Question 7

.filter()

Answer 7

The filter() method creates a new array with all elements that pass the test implemented by the provided function.

Question 8

.find()

Answer 8

The find() method returns the value of the first element in the provided array that satisfies the provided testing function. If no values satisfy the testing function, undefined is returned.

Question 9

.findIndex()

Answer 9

The findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise, it returns -1, indicating that no element passed the test.

Question 10

.flat()

Answer 10

The flat() method creates a new array with all sub-array elements concatenated into it recursively up to the specified depth.

Question 11

.flatMap()

Answer 11

The flatMap() method 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. It is identical to a map() followed by a flat() of depth 1, but slightly more efficient than calling those two methods separately.

Question 12

.forEach()

Answer 12

The forEach() method executes a provided function once for each array element.

Question 13

.from()

Answer 13

The Array.from() static method creates a new, shallow-copied Array instance from an array-like or iterable object.

Question 14

.includes()

Answer 14

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

Question 15

.indexOf()

Answer 15

The indexOf() method returns the first index at which a given element can be found in the array, or -1 if it is not present.

Question 16

.isArray()

Answer 16

The Array.isArray() method determines whether the passed value is an Array.

Question 17

.join()

Answer 17

The join() method creates and returns a new string by concatenating all of the elements in an array (or an array-like object), separated by commas or a specified separator string. If the array has only one item, then that item will be returned without using the separator.

Question 18

.keys()

Answer 18

The keys() method returns a new Array Iterator object that contains the keys for each index in the array.

Question 19

.lastIndexOf()

Answer 19

The lastIndexOf() method returns the last index at which a given element can be found in the array, or -1 if it is not present. The array is searched backwards, starting at fromIndex.

Question 20

.map()

Answer 20

The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.

Question 21

Array.of()

Answer 21

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

The difference between Array.of() and the Array constructor is in the handling of integer arguments: Array.of(7) creates an array with a single element, 7, whereas Array(7) creates an empty array with a length property of 7 (Note: this implies an array of 7 empty slots, not slots with actual undefined values).

Question 22

.pop()

Answer 22

The pop() method removes the last element from an array and returns that element. This method changes the length of the array.

Question 23

.push()

Answer 23

The push() method adds one or more elements to the end of an array and returns the new length of the array.

Question 24

.reduce()

Answer 24

The reduce() method executes a user-supplied “reducer” callback function on each element of the array, 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.

Perhaps the easiest-to-understand case for reduce() is to return the sum of all the elements in an array.

The reducer walks through the array element-by-element, at each step adding the current array value to the result from the previous step (this result is the running sum of all the previous steps) — until there are no more elements to add.

Question 25

.reduceRight()

Answer 25

The reduceRight() method applies a function against an accumulator and each value of the array (from right-to-left) to reduce it to a single value.

Question 26

.reverse()

Answer 26

The reverse() method reverses an array in place. The first array element becomes the last, and the last array element becomes the first.

Question 27

.shift()

Answer 27

The shift() method removes the first element from an array and returns that removed element. This method changes the length of the array.

Question 28

.slice()

Answer 28

The slice() method returns a shallow copy of a portion of an array into a new array object selected from start to end (end not included) where start and end represent the index of items in that array. The original array will not be modified.

Question 29

.some()

Answer 29

The some() method tests whether at least one element in the array passes the test implemented by the provided function. It returns true if, in the array, it finds an element for which the provided function returns true; otherwise it returns false. It doesn’t modify the array.

Question 30

.sort()

Answer 30

The sort() method sorts the elements of an array in place and returns the sorted array. The default sort order is ascending, built upon converting the elements into strings, then comparing their sequences of UTF-16 code units values.

The time and space complexity of the sort cannot be guaranteed as it depends on the implementation.

Question 31

.splice

Answer 31

The splice() method changes the contents of an array by removing or replacing existing elements and/or adding new elements in place. To access part of an array without modifying it, see slice().

Question 32

toLocaleString()

Answer 32

The toLocaleString() method returns a string representing the elements of the array. The elements are converted to Strings using their toLocaleString methods and these Strings are separated by a locale-specific String (such as a comma “,”).

Question 33

toLocaleString()

Answer 33

The toLocaleString() method returns a string representing the elements of the array. The elements are converted to Strings using their toLocaleString methods and these Strings are separated by a locale-specific String (such as a comma “,”).

Question 34

toString()

Answer 34

The toString() method returns a string representing the specified array and its elements.

Question 35

.unshift()

Answer 35

The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array.

Question 36

.value()

Answer 36

The values() method returns a new array iterator object that contains the values for each index in the array.