Array Methods

Question 1

let arr = [“I”, “go”, “home”];
delete arr[1];
alert( arr[1] ); // returns?

Answer 1

undefined

That’s natural, because delete obj.key removes a value by the key. It’s all it does. Fine for objects. But for arrays we usually want the rest of elements to shift and occupy the freed place. We expect to have a shorter array now.

Question 2

let arr = [“I”, “go”, “home”];
delete arr[1];
alert( arr.length ); // returns?

Answer 2

3

now arr = [“I”, , “home”];

Question 3

let arr = [“I”, “study”, “JavaScript”];
arr.splice(1, 1);
alert( arr ); // returns?

Answer 3

[“I”, “JavaScript”]

Question 4

let arr = [“I”, “study”, “JavaScript”, “right”, “now”];
arr.splice(0, 3, “Let’s”, “dance”);

alert( arr ) // returns?

Answer 4

[“Let’s”, “dance”, “right”, “now”]

Question 5

let arr = [“I”, “study”, “JavaScript”, “right”, “now”];

let removed = arr.splice(0, 2);

alert( removed ); // returns?

Answer 5

“I”, “study” <– array of removed elements

Question 6

let arr = [“I”, “study”, “JavaScript”];

arr.splice(2, 0, “complex”, “language”);

alert( arr ); // returns?

Answer 6

“I”, “study”, “complex”, “language”, “JavaScript”

Question 7

The method ________creates a new array that includes values from other arrays and additional items.

Answer 7

arr.concat

Question 8

The _______ method allows to run a function for every element of the array.

Answer 8

arr.forEach

Question 9

_______– looks for item starting from index from, and returns the index where it was found, otherwise -1.

Answer 9

arr.indexOf(item, from)

Question 10

________item, from) – looks for item starting from index from, returns true if found.

Answer 10

arr.includes()

Question 11

let arr = [1, 0, false];

alert( arr.indexOf(0) ); //
alert( arr.indexOf(null) ); //

Answer 11

1

-1

Question 12

The method _______ is the same as indexOf, but looks for from right to left.

Answer 12

arr.lastIndexOf

Question 13

Imagine we have an array of objects. How do we find an object with the specific condition?

Answer 13

arr.find(fn)

let result = arr.find(function(item, index, array) {
// if true is returned, item is returned and iteration is stopped
// for falsy scenario returns undefined
});

Question 14

et users = [
{id: 1, name: “John”},
{id: 2, name: “Pete”},
{id: 3, name: “Mary”}
];

let user = users.find( );
write code

alert(user.name); // John

Answer 14

item => item.id == 1

Question 15

const arr = [NaN];
alert( arr.indexOf(NaN) ); //
alert( arr.includes(NaN) );//

Answer 15

-1

true (correct)

Question 16

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

Answer 16

map()

Question 17

let lengths = [“Bilbo”, “Gandalf”, “Nazgul”].map(item => item.length);
alert(lengths); //

Answer 17

5,7,6

Question 18

let lengths = [“Bilbo”, “Gandalf”, “Nazgul”]

using map return results

alert(lengths); // 5,7,6

Answer 18

.map(item => item.length);

Question 19

The _____method sorts the elements of an array in place and returns the reference to the same array, now sorted.

Answer 19

sort()

Question 20

let arr = [ 1, 2, 15 ];

arr.sort();

alert( arr ); //

Answer 20

1, 15, 2

Question 21

in arrays all elements are converted to ______ for comparisons.

Answer 21

strings

Question 22

let arr = [1, 2];
alert( arr.concat([3, 4], 5, 6) ); //

Answer 22

1,2,3,4,5,6

Question 23

let arr = [1, 2];

let arrayLike = {
0: “something”,
length: 1
};

alert( arr.concat(arrayLike) ); //

Answer 23

1,2,[object Object]

Question 24

The _____method creates a shallow copy of a portion of a given array, filtered down to just the elements from the given array that pass the test implemented by the provided function

Answer 24

filter()

Question 25

let arr = [ 1, 2, 15 ];

arr.sort
// write the sort function

alert(arr); // 1, 2, 15

Answer 25

(function(a, b) { return a - b; });

Question 26

arr.sort(function(a, b) { return a - b; });

WRITE AS AN ARROW

Answer 26

arr.sort( (a,b) => a - b );

Question 27

in arrays For many alphabets, it’s better to use _______ method to correctly sort letters

Answer 27

str.localeCompare

Question 28

The method ________reverses the order of elements in arr.

Answer 28

arr.reverse

Question 29

The _______method takes a pattern and divides a String into an ordered list of substrings by searching for the pattern, puts these substrings into an array, and returns the array

Answer 29

split()

Question 30

let str = “test”;

alert( str.split(‘’) ); //

Answer 30

t,e,s,t

Question 31

The ______ method takes a pattern and divides a String into an ordered list of substrings by searching for the pattern, puts these substrings into an array, and returns the array.

Answer 31

split()

Question 32

The_______ 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.

Answer 32

join()

Question 33

let arr = [‘Bilbo’, ‘Gandalf’, ‘Nazgul’];

let str =
// glue the array into a string using ;

alert( str ); // Bilbo;Gandalf;Nazgul

Answer 33

arr.join(‘;’);

Question 34

let arr = [‘Bilbo’, ‘Gandalf’, ‘Nazgul’];

let str = arr.join(‘;’); // glue the array into a string using ;

alert( str ); //

Answer 34

Bilbo;Gandalf;Nazgul

Question 35

When we need to iterate and return the data for each element – we can use

Answer 35

map.

Question 36

When we need to iterate over an array – we can use name all 3

Answer 36

for
for…of
for Each

Question 37

let arr = [1, 2, 3, 4, 5];

let result = arr.reduce((sum, current) => sum + current, 0);

alert(result); // returns and why

Answer 37

15

Question 38

let arr = [1, 2, 3, 4, 5];

// removed initial value from reduce (no 0)
let result = arr.reduce((sum, current) => sum - current);

alert( result ); //

Answer 38

-13

Question 39

let arr = [1, 2, 3, 4, 5];

let result = arr.reduce((sum, current) => sum + current, 4);

alert(result); //

Answer 39

19

Question 40

alert(typeof {}); //

Answer 40

object

Question 41

alert(typeof []); //

Answer 41

object

Question 42

alert(Array.isArray({})); //true or false

Answer 42

false

Question 43

alert(Array.isArray([])); // true or false

Answer 43

true