Arrays

Question 1

What is an ordered collection of values?

Answer 1

An Array

Question 2

What is an element of an array?

Answer 2

Each value in the array

Question 3

What are array indexes?

Answer 3

It is the numeric position of the element in the array

Question 4

What does it mean to JavaScript arrays are untyped?

Answer 4

An array element may be of any type, and different elements of the same array may be of different types.

Question 5

Can array elements be objects or other arrays?

Answer 5

Yes

Question 6

What are some properties of Arrays in JavaScript?

Answer 6

• Ordered collection of values
• Specialized form of Object (array indexes are like properties)
• Arrays are dynamic: grow or shrink as needed
• JavaScript arrays are untyped
• Array elements may be objects or other array
• Are zero-based and use 32-bit indexes (Highest posible index 2↑32 - 2)

Question 7

What does it mean that JavaScript Arrays may be sparse?

Answer 7

The elements not need to have contiguous indexes, and ther may be gaps.

Question 8

let array = [10,2,,5,1]

What is the .length?

Answer 8

5

Question 9

let array = [,,]

What is the .length?

Answer 9

2

Question 10

What are the four ways to create arrays?

Answer 10

• Array literals
• … spread operator
• Array() constructor
• Array.of() and Array.from() factory methods

Question 11

What is an Array literal?

Answer 11

comma-separated list of array elements within square brackets
~~~
let empty = [];
let primes = [2,3,4,7,11];
~~~

Question 12

Is the following code valid? Why?
~~~
let base = 1024;
let table = [base, base + 1, base +2, base + 3];
~~~

Answer 12

It is valid because array literal values need NOT to be constants.

Question 13

What does the following code print?

let array = [10,2,,5,1]
console.log(array[2]); 

Answer 13

undefined

Question 14

What is missing the make the following code valid?

let a = [1, 2, 3];
let b = [0, ?, 4];
// b == [1, 2, 3, 4]

Answer 14

The spread operator in line 2
~~~
let a = [1, 2, 3];
let b = [0, …a, 4]; // notice …a
// b == [1, 2, 3, 4]
~~~

Question 15

How to create a copy of the following array using the spread operator?

let original = [1, 2, 3];

Answer 15

let original = [1, 2, 3];
let copy = [...original];

Modifying the copy does not change the original

Question 16

How can I turn the following string into an array of single-char array?

let letters = "abcde123";

Answer 16

let letters = "abcde123";
let arrayOfCharacters = [...letters]

Strings are iterable

Spread operator works on any iterable object

Question 17

What does the following code do?

let letters = [..."hello world"];
[...new Set(letters)]

Answer 17

It removes duplicates from the array resulting in:
~~~
// => [“h”, “e”, “l”, “o”, “ “, “w”, “r”, “d”]
~~~