Mozilla "Array"

Question 1

The ________ method creates a new, shallow-copied Array instance from an array-like or iterable object

Answer 1

Array.from()

Question 2

console.log((\_\_\_\_\_\_\_\_\_\_'foo'));
// expected output: Array ["f", "o", "o"]

console.log(\_\_\_\_\_\_\_\_\_\_\_([1, 2, 3], x => x * x));
// expected output: Array [2, 4, 6]

Answer 2

Array.from

Question 3

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

Answer 3

concat()

Question 4

var array1 = ['a', 'b', 'c'];
var array2 = ['d', 'e', 'f'];

console.log(array1.\_\_\_\_\_\_\_\_(array2));
// expected output: Array ["a", "b", "c", "d", "e", "f"]

Answer 4

concat

Question 5

var array1 = ['a', 'b', 'c'];
var array2 = ['d', 'e', 'f'];

console.log(\_\_\_\_\_\_\_\_\_\_\_\_\_);
// expected output: Array ["a", "b", "c", "d", "e", "f"]

Answer 5

array1.concat(array2)

Question 6

The_______method creates a new Array instance from a variable number of arguments, regardless of number or type of the arguments.

Answer 6

Array.of()

Question 7

The ___________ method determines whether the passed value is an Array.

Answer 7

Array.isArray()

Question 8

Array.of(7); //

Answer 8

[7]

Question 9

Array(7) //

Answer 9

[ , , , , , , ]

Question 10

console.log(Array.\_\_\_\_\_([1, 2, 3], x => x + x));
// expected output: Array [2, 4, 6]

Answer 10

from

Question 11

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. If the array has only one item, then that item will be returned without using the separator.

Answer 11

join()

Question 12

var elements = [‘Fire’, ‘Air’, ‘Water’];

console.log(elements.join());
// expected output: 

console.log(elements.join('-'));
// expected output:

Answer 12

“Fire,Air,Water”

“Fire-Air-Water”

Question 13

var elements = [‘Fire’, ‘Air’, ‘Water’];

console.log(\_\_\_\_\_\_\_\_\_\_\_\_);
// expected output: "Fire-Air-Water"

Answer 13

elements.join(‘-‘)

Question 14

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

Answer 14

keys()

Question 15

The __________ method reverses an array in place. The first array element becomes the last, and the last array element becomes the first.

Answer 15

reverse()

Question 16

The _______ method creates and returns a new string, the ______ method a array

Answer 16

join()

concat()

Question 17

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

Answer 17

every()

Question 18

The every() returns a _________

Answer 18

Boolean value.

Question 19

function isBelowThreshold(currentValue) {
  return currentValue < 40;
}

var array1 = [1, 30, 39, 29, 10, 13];

console.log(\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_);
// expected output: true

Answer 19

array1.every(isBelowThreshold)

Question 20

Array.of(7); //

Array.of(1, 2, 3); //

Answer 20

[7]

[1, 2, 3]

Question 21

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

Answer 21

sort()

Question 22

The _________ method returns a string representing the specified array and its elements.

Answer 22

toString()

Question 23

var array1 = [1, 2, ‘a’, ‘1a’];

console.log(\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_);
// expected output: "1,2,a,1a"

Answer 23

array1. toString()

array1. join()

Question 24

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

Answer 24

includes()

Question 25

includes() returns _________?

Answer 25

true or false

Question 26

2 ways of creating array

let arr =
let arr =

Answer 26

new Array();
[];

Question 27

let fruits = ["Apple", "Orange", "Plum"];
fruits[2] = 'Pear'; //

Answer 27

now [“Apple”, “Orange”, “Pear”]

Question 28

let fruits = ["Apple", "Orange", "Plum"];
fruits[3] = 'Lemon';

Answer 28

// now [“Apple”, “Orange”, “Pear”, “Lemon”]

Question 29

let fruits = [“Banana”]

let arr = fruits;

alert( arr === fruits ); //

Answer 29

true

Question 30

let fruits = [“Apple”, “Orange”, “Plum”];

// iterates over array elements USING FOR OF

Answer 30

for (let fruit of fruits) {
alert( fruit );
}

Question 31

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

arr.length = 2;
alert( arr ); // [1, 2]

arr.length = 5; // return length back
alert( arr[3] ); // ??

Answer 31

undefined: the values do not return

Question 32

simplest way to clear the array is _______

Answer 32

arr.length = 0;

Question 33

let arr = new Array(2)

alert( arr[0] ); //

Answer 33

undefined! no elements.

Question 34

let arr = new Array(2); // will it create an array of [2] ?

alert( arr.length ); //

Answer 34

length 2

Question 35

let arr = [“I”, “go”, “home”];

delete arr[1];

alert( arr[1] ); //

alert( arr.length ); //

Answer 35

undefined

3

Question 36

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

Answer 36

forEach

Question 37

arr.forEach(function(\_\_\_\_ , \_\_\_\_\_\_\_\_ , \_\_\_\_\_\_\_) {
  // ... do something with item
});

Answer 37

item, index, array

Question 38

3 search methods for array

Answer 38

indexOf,
lastIndexOf
includes

Question 39

let arr = [1, 0, false];

alert( arr.indexOf(0) ); //
alert( arr.indexOf(false) ); //
alert( arr.indexOf(null) ); //
alert( arr.includes(1) ); //

Answer 39

1

2

-1

true

Question 40

let result = arr.find(function(__ , ______ , ______) {

});

returns

Answer 40

item, index, array

Question 41

let users = [
  {id: 1, name: "John"},
  {id: 2, name: "Pete"},
  {id: 3, name: "Mary"}
];

let user = users.find(item => item.id == 2);

alert(user.name); //

Answer 41

Pete

Question 42

let users = [
  {id: 1, name: "John"},
  {id: 2, name: "Pete"},
  {id: 3, name: "Mary"}
];

let user = users.find(_____________);

alert(user.name); // John

Answer 42

item => item.id == 1

Question 43

var myA1 = [1,2,3];
var myA2 = [1,2,3];

console.log(myA1==myA2);

Answer 43

false

Question 44

let arr = [ 1, 2, 15 ];

// the method reorders the content of arr (and returns it)
arr.sort();

alert( arr ); //

Answer 44

1, 15, 2

Question 45

let arr = [ 1, 2, 15, 155 ];

arr.sort();

alert( arr );

Answer 45

1, 15, 155, 2

Question 46

“2” > “15”

Answer 46

TRUE

Question 47

function compareNumeric(a, b) {
  if (a > b) return 
  if (a == b) return 
  if (a < b) return 
}

Answer 47

1

0

-1

Question 48

let str = “test”;

alert(________); // t,e,s,t

Answer 48

str.split(‘’)

Question 49

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

Answer 49

forEach, for or for..of.

Question 50

The ____________ method executes a provided function once for each array element.

Answer 50

forEach()

Question 51

_________— executes a provided function once for each array element.
__________— creates a new array with the results of calling a provided function on every element in the calling array.

Answer 51

forEach() 

map() 

Question 52

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

Answer 52

copyWithin()

Question 53

copyWithin()

Answer 53

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

arr.copyWithin(target[, start[, end]])

Question 54

var array1 = [‘a’, ‘b’, ‘c’, ‘d’, ‘e’];

console.log(array1.copyWithin(0, 3, 4));
// expected output:

Answer 54

Array [“d”, “b”, “c”, “d”, “e”]

Question 55

var array1 = [‘a’, ‘b’, ‘c’, ‘d’, ‘e’];

console.log(array1.copyWithin(1, 3));
// expected output:

Answer 55

Array [“d”, “d”, “e”, “d”, “e”]

Question 56

arr.copyWithin(________)

Answer 56

target[, start[, end]]

Question 57

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

Answer 57

indexOf()

Question 58

var beasts = [‘ant’, ‘bison’, ‘camel’, ‘duck’, ‘bison’];

console.log(beasts.indexOf('bison'));
// expected output:

Answer 58

1

Question 59

var beasts = [‘ant’, ‘bison’, ‘camel’, ‘duck’, ‘bison’];

// start from index 2
console.log(beasts.indexOf('bison', 2));
// expected output:

Answer 59

4

Question 60

var beasts = [‘ant’, ‘bison’, ‘camel’, ‘duck’, ‘bison’];

console.log(beasts.indexOf('giraffe'));
// expected output:

Answer 60

// expected output: -1

Question 61

arr.indexOf(_________[,__________])

Answer 61

searchElement

fromIndex

Question 62

var array1 = [1, 2, 3];

console.log(array1);
// expected output:

Answer 62

Array [1, 2, 3]

Question 63

arr.copyWithin(______[,________[, ______]])

Answer 63

target . start . end

Question 64

USE .some or .every?

const userPrivileges = ['user', 'user', 'user', 'admin'];
const containsAdmin = userPrivileges.\_\_\_\_\_\_\_( element => element === 'admin');
// containsAdmin will be equal to true

Answer 64

some

Question 65

use .some or .every?

const ratings = [3, 5, 4, 3, 5];
const goodOverallRating = ratings.\_\_\_\_\_\_( rating => rating >= 3 );
// goodOverallRating will be equal to true

Answer 65

every

Question 66

const icecreamColors = {
    chocolate: 'brown',
    vanilla: 'white',
    strawberry: 'red',
}

const colors =\_\_\_\_\_\_\_\_\_\_;
// colors will be equal to ["brown", "white", "red"]

Answer 66

Object.values(icecreamColors)

Question 67

const icecreamColors = {
  chocolate: 'brown',
  vanilla: 'white',
  strawberry: 'red',
}

const types = \_\_\_\_\_\_\_\_\_
// types will be equal to ["chocolate", "vanilla", "strawberry"]

Answer 67

Object.keys(icecreamColors);

Question 68

var arr = [[1,2], [3,4], [5,6]];
alert the number 5

Answer 68

alert(arr[2][0]);

Question 69

The _________ method tests whether at least one element in the array passes the test implemented by the provided function. It returns a Boolean value.

Answer 69

some()

Question 70

The _________ 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.

Answer 70

lastIndexOf()

Question 71

var animals = ['Dodo', 'Tiger', 'Penguin'];
console.log(animals.lastIndexOf('Penguin'));
// expected output: 

console.log(animals.lastIndexOf('Dodo'));
// expected output:

Answer 71

2

0

Question 72

The___________ method fills (modifies) all the elements of an array from a start index (default zero) to an end index (default array length) with a static value. It returns the modified array.

Answer 72

fill()

Question 73

var array1 = [1, 2, 3, 4];

array1.fill(6) returns

Answer 73

// expected output: [6, 6, 6, 6]

Question 74

var array1 = [1, 2, 3, 4];

console.log(array1.fill(0, 2, 4));

Answer 74

// expected output: [1, 2, 0, 0]

// fill with 0 from position 2 until position 4

Question 75

var array1 = [1, 2, 3, 4];
console.log(array1.fill(5, 1));

Answer 75

// expected output: [1, 5, 5, 5]

Question 76

var array = [2, 9, 9];

array.indexOf(7); //

Answer 76

-1

Question 77

var array = [2, 9, 9];

array.indexOf(9, 2); //

Answer 77

2

Question 78

var array = [2, 9, 9];
array.indexOf(2, -1); //

Answer 78

-1

Question 79

var array = [2, 9, 9];
array.indexOf(2, -3); //

Answer 79

0

Question 80

__________syntax allows an iterable such as an array expression or string to be expanded in places where zero or more arguments (for function calls) or elements (for array literals) are expected, or an object expression to be expanded in places where zero or more key-value pairs (for object literals) are expected.

Answer 80

Spread operator

Question 81

function sum(x, y, z) {
  return x + y + z;
}

const numbers = [1, 2, 3];

console.log(sum(...numbers));
// expected output:

Answer 81

6

Question 82

function sum(x, y, z) {
  return x + y + z;
}

const numbers = [1, 2, 3];

console.log(sum.apply(null, numbers));
// expected output:

Answer 82

6

Question 83

Concating these two arrays will result//

my arr1 = [[“steve”, 33],[“me”, 22]]
my arr2 = [“john”, 55]

Answer 83

[[“steve”, 33],[“me”, 22], “john”, 55]

Question 84

Concating these two arrays will result//

my arr1 = [[“steve”, 33],[“me”, 22]]
my arr2 = [[“john”, 55]]

Answer 84

[[“steve”, 33],[“me”, 22], [“john”, 55]]

Question 85

let array1 = [1,2,3];
let array2 = [4,5,6];
let array3 = // concat using … spread syntax

Answer 85

[…array1,…array2];

Question 86

let array1 = [1,2,3];
let array2 = [4,5,6];
let array3 = // concat using concat()

Answer 86

console.log(array1.concat(array2));

Question 87

var blue = {
color:blue;
}

let colors = [{color:red}, {color:blue}];

var index = indexOf(blue) // returns

Answer 87

-1

referencing the blue object

Question 88

var blue = {
color:blue;
}

let colors = [{color:red}, blue];

var index = indexOf(blue) // returns

Answer 88

1

referencing from array

Question 89

arr.indexOf(_________)

Answer 89

searchElement[, fromIndex]