Map and Set

Question 1

_____are used for storing keyed collections.

______are used for storing ordered collections.

Answer 1

Objects
Arrays

Question 2

Map is a collection of keyed data items, just like an Object. But the main difference is that Map allows_______

Answer 2

keys of any type.

Question 3

unlike objects, keys are not converted to ______

Answer 3

unlike objects, keys are not converted to strings

Question 4

creates the map

Answer 4

new Map()

Question 5

The method sets and stores the value by the key.

Answer 5

map.set(key, value)

Question 6

returns the value by the key, undefined if key doesn’t exist in map.

Answer 6

map.get(key) –

Question 7

returns true if the key exists, false otherwise.

Answer 7

map.has(key)

Question 8

removes the element (the key/value pair) by the key.

Answer 8

map.delete(key) –

Question 9

removes everything from the map

Answer 9

map.clear()

Question 10

returns the current element count.

Answer 10

map.size

Question 11

Map can also use objects as _____

Answer 11

keys

Question 12

let john = { name: “John” };

let visitsCountMap = new Map();

set map to return below

alert( visitsCountMap.get(john) ); // 123

Answer 12

visitsCountMap.set(john, 123);

Question 13

For looping over a map, there are 3 methods:

Answer 13

map.keys() – returns an iterable for keys,

map.values() – returns an iterable for values,

map.entries() – returns an iterable for entries [key, value], it’s used by default in for..of.

Question 14

let recipeMap = new Map([
[‘cucumber’, 500],
[‘tomatoes’, 350],
[‘onion’, 50]
]);

// iterate over keys (vegetables)

Answer 14

for (let vegetable of recipeMap.keys()) {
alert(vegetable); // cucumber, tomatoes, onion
}

Question 15

let recipeMap = new Map([
[‘cucumber’, 500],
[‘tomatoes’, 350],
[‘onion’, 50]
]);

// iterate over values (amounts)

Answer 15

for (let amount of recipeMap.values()) {
alert(amount); // 500, 350, 50
}

Question 16

let recipeMap = new Map([
[‘cucumber’, 500],
[‘tomatoes’, 350],
[‘onion’, 50]
]);

// iterate over [key, value] entries

Answer 16

for (let entry of recipeMap) { // the same as of recipeMap.entries()
alert(entry); // cucumber,500 (and so on)
}

Question 17

The iteration goes in the same order as the values were inserted. Map preserves this order, unlike a regular Object.

true or false

Answer 17

true

Question 18

let map = new Map([
[‘1’, ‘str1’],
[1, ‘num1’],
[true, ‘bool1’]
]);

alert( map.get(‘1’) ); //

Answer 18

str1

Question 19

let map = new Map([
[‘1’, ‘str1’],
[1, ‘num1’],
[true, ‘bool1’]
]);

alert( ________ ); // true
what code to write?

Answer 19

map.get(true)

Question 20

let obj = {
name: “John”,
age: 30
};

let map = new Map(Object.entries(obj));

alert( map.get(‘name’) ); //

Answer 20

John

Question 21

let obj = {
name: “John”,
age: 30
};

let map =

alert( map.get(‘name’) ); // John

Answer 21

new Map(Object.entries(obj));

Question 22

_____________ method that does the reverse: given an array of [key, value] pairs, it creates an object from them:

Answer 22

Object.fromEntries

Question 23

let prices = Object.fromEntries([
[‘banana’, 1],
[‘orange’, 2],
[‘meat’, 4]
]);

// now prices =

Answer 23

{ banana: 1, orange: 2, meat: 4 }

Question 24

let prices = Object.fromEntries([
[‘banana’, 1],
[‘orange’, 2],
[‘meat’, 4]
]);

// now prices = { banana: 1, orange: 2, meat: 4 }

alert(prices.orange); //

Answer 24

2

Question 25

let set = // create new empty set

Answer 25

new Set()

Question 26

let set = new Set();

let john = { name: “John” };
let pete = { name: “Pete” };
let mary = { name: “Mary” };

// visits, some users come multiple times
set.add(john);
set.add(pete);
set.add(mary);
set.add(john);
set.add(mary);

// set keeps only unique values
alert( set.size ); // returns and why

Answer 26

3

keeps only unique values

Question 27

______– adds a value, returns the set itself.

Answer 27

set.add(value)

Question 28

__________– removes the value, returns true if value existed at the moment of the call, otherwise false.

Answer 28

set.delete(value)

Question 29

___________– returns true if the value exists in the set, otherwise false.

Answer 29

set.has(value)

Question 30

______________ removes everything from the set.

Answer 30

set.clear() –

Question 31

__________ – is the elements count.

Answer 31

set.size

Question 32

We can loop over a set either with

Answer 32

for..of
forEach:

Question 33

let set = new Set();

let john = { name: “John” };
let pete = { name: “Pete” };
let mary = { name: “Mary” };

set.add(john);
set.add(pete);
set.add(mary);

for (let user of set) {
alert(user.name); //
}

Answer 33

John (then Pete and Mary)

Question 34

let set = new Set();

let john = { name: “John” };
let pete = { name: “Pete” };
let mary = { name: “Mary” };

set.add(john);
set.add(pete);
set.add(mary);