Maps

Question 1

An Object has a prototype, so there are default keys in the map. However, this can be bypassed using map = __________.

Answer 1

Object.create(null)

Question 2

The keys of an objects are __________, where they can be any value for a Map.

Answer 2

strings

Question 3

Maps can be iterated using a

Answer 3

for..of loop:

Question 4

ITERATE THROUGH THIS MAP for of

var myMap = new Map();
myMap.set(0, ‘zero’);
myMap.set(1, ‘one’);

// CODE HERE

// 0 = zero
// 1 = one

Answer 4

for (var [key, value] of myMap) {
console.log(key + ‘ = ‘ + value);
}

Question 5

ITERATE THROUGH THIS MAP for of

var myMap = new Map();
myMap.set(0, ‘zero’);
myMap.set(1, ‘one’);

// CODE HERE

// 0
// 1

Answer 5

for (var key of myMap.keys()) {
console.log(key);
}

Question 6

ITERATE THROUGH THIS MAP for of

var myMap = new Map();
myMap.set(0, ‘zero’);
myMap.set(1, ‘one’);

// CODE HERE

// zero
// one

Answer 6

for (var value of myMap.values()) {
console.log(value);
}

Question 7

ITERATE THROUGH THIS MAP forEach

var myMap = new Map();
myMap.set(0, ‘zero’);
myMap.set(1, ‘one’);

// CODE HERE

// Will show 2 logs; first with “0 = zero” and second with “1 = one”

Answer 7

myMap.forEach(function(value, key) {
console.log(key + ‘ = ‘ + value);
});

Question 8

var original = new Map([
[1, ‘one’]
]);

var clone = new Map(original);

console. log(clone.get(1)); //
console. log(original === clone); //

Answer 8

one

false. Useful for shallow comparison

Question 9

let ages = new Map();

SET key to “Boris” and “Value” to 39

Answer 9

ages.set(“Boris”, 39);

Question 10

____________are special objects per se, they are iterables with key value pair constructor that looks like a 2D array but acts like an object. They offer a better flexibility in terms of choosing our key values. A ______ can have a key value which can be a string, number, object or even NaN.

Answer 10

Maps

Maps

Question 11

The _________method removes all elements from a Set object.

Answer 11

clear()

Question 12

in a ____ you can not have 2 of the same items

Answer 12

set

Question 13

convert a set to array 
const myArray =

Answer 13

array.from(name of set)

Question 14

var myMap = new Map();
myMap.set(‘0’, ‘foo’);
myMap.set(1, ‘bar’);
myMap.set({}, ‘baz’);

var mapIter = myMap.keys();

console. log(________________); // “0”
console. log(_________________); // 1
console. log(_________________; // Object

Answer 14

mapIter.next().value
mapIter.next().value
mapIter.next().value

Question 15

The _______ method executes a provided function once per each key/value pair in the Map object, in insertion order.

Answer 15

forEach()

Question 16

This iterates over a list and applies some operation with side effects to each list member (example: saving every list item to the database)

Answer 16

forEach()

Question 17

This iterates over a list, transforms each member of that list, and returns another list of the same size with the transformed members (example: transforming list of strings to uppercase)

Answer 17

map

Question 18

The _____ method returns a specified element from a Map object.

Answer 18

get()

Question 19

_______ – creates the map.

Answer 19

new Map()

Question 20

________ – stores the value by the key.

Answer 20

map.set(key, value)

Question 21

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

Answer 21

map.get(key) –

Question 22

__________– returns true if the key exists, false otherwise.

Answer 22

map.has(key)

Question 23

_________– removes the value by the key.

Answer 23

map.delete(key) – removes the value by the key.

Question 24

_________– clears the map

Answer 24

map.clear()

Question 25

_________ – returns the current element count.

Answer 25

map.size

Question 26

“chain” the calls:

let map = new Map();

map. set(‘1’, ‘str1’);
map. set(1, ‘num1’);
map. set(true, ‘bool1’);

Answer 26

map.set(‘1’, ‘str1’)
.set(1, ‘num1’)
.set(true, ‘bool1’);

Question 27

For looping over a map, there are 3 methods:

Answer 27

map. keys()
map. values()
map. entries()

Question 28

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

Answer 28

for..of.

Question 29

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

Answer 29

map.entries()

Question 30

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

for (let vegetable of recipeMap.keys()) {
alert(vegetable); //
}

Answer 30

cucumber, tomatoes, onion

Question 31

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

for (let vegetable of recipeMap.values()) {
alert(vegetable); //
}

Answer 31

500, 350, 50