Array Knowledge

Question 1

Shallow copy array, 4 ways

Why are they able to copy an array and what are they meant to do?

Answer 1

let newObj = oldObj.slice(first index, upper non inc index)

let newObj = oldObj .filter(function boolean goes to newObj)

let newObj = [ …oldObj]
spread syntax

let newObj = Array.from(string using the string letters as indexes or array, function return goes to new array with same indexes)

Question 2

Create an array, 2 ways

Answer 2

let myArray = [ ]
let myArray = new Array(1, 2, ['nested array'])

Question 3

Return array item

Answer 3

myArray[ ]

Question 4

Return last element from array

Answer 4

myArray[myArray.length-1]

Question 5

Create and return array properties

Answer 5

The same way as you would an object because arrays are objects.
These properties just don’t function with array index syntax and array methods that rely on indexes.

create
myArray[‘myKey’] = ‘my value’
or
myArray.myKey = ‘my value’

return with myArray.myKey or myArray[‘myKey’]

Question 6

1.
Return THE INDEX AS A NUMBER of the first specific value in an array if it === with the argument
The second argument indicates which element to start looking from

2.
Can you do regex?

3.
What’s another one that returns the index but searches from the end of an array?

4.
What’s another one that returns the index but searches based on a callback function?

Answer 6

myArray.indexOf (searchelement, from index)
can’t do / /g

myArray.lastIndexOf(searchelement, from index )

myArray.findIndex(callback function)

Question 7

Change an array element

Answer 7

myArray[old index] = ‘new element’

Question 8

Add an array element to a specific index

Answer 8

myArray[new index] = ‘new element’

Question 9

Return an array based off an array-like object argument .

The second argument can be a callback function. The function’s return is mapped onto the new array.

Answer 9

newArray = Array.from(myArray, callbackfunction)

Question 10

Write function to compare arrays for shallow equality

Answer 10

function arraysEqual(arr1, arr2) {
  if (arr1.length !== arr2.length) return false;

  for (let i = 0; i < arr1.length; i += 1) {
    if (arr1[i] !== arr2[i]) {
      return false;
    }
  }

return true;
}

Question 11

Why do array elements start at 0?

Answer 11

It’s how many elements away from the first element. Most programming languages behave this way.

Question 12

What is returned from
let anArray = [1, 2, 3]
anArray[1,2]
?

Answer 12

3

Question 13

Having a comma at the end of an array or object is fine
let fruits = [
  "Apple",
  "Orange",
  "Plum",
];

t or f

Answer 13

T

AND it makes it easier to add more later a little bit

Question 14

Add and call a function as an array element

Answer 14

let arr = [ 
  function() { 
    console.log('hello'); 
    console.log('goodbye');
  } ];
arr[0]()

Question 15

Difference between queue and stack in terms of arrays.

Answer 15

Add to end, take from start.
Stack, LIFO (Last-In-First-Out) principle,

Add to end, take from end
Queue, FIFO(First in First out) principle

Question 16

What is a deque?

Answer 16

A Double-ended queue.

Like arrays in JS

Question 17

What is another terms for things like Arrays in JS that allow adding and removing elements from either end?

Answer 17

deque

double ended queues

Question 18

What happens if you misuse an array?
The ways to misuse an array:
Add a non-numeric property like arr.test = 5.
Make holes, like: add arr[0] and then arr[1000] (and nothing between them).
Fill the array in the reverse order, like arr[1000], arr[999] and so on.

Answer 18

Regularly arrays try to store data contiguously (beside one another in memory).
They stop doing this if you use them like normal objects or have large gaps or fill them in reverse order.

Question 19

Why is it so much faster to work with the end of an array rather than the beginning?

Answer 19

Have to move all elements when adding or subtracting from the beginning of the array.
The longer the array the longer it will take