Array Functions

Question 1

Create an array from a string.

Answer 1

const someStr = ‘hello world’;

• Array.from(someStr);
• […someStr]
• someStr.split(‘’);
• Object.assign([], string);

Question 2

Create an array with a function to map every element of the array.

Answer 2

Array.from([1, 2, 3], x => x + 1);

Question 3

Create array with a number of empty slots

Answer 3

Array(3);

Question 4

Initialize an array with values

Answer 4

Array.of(1, 2, 3);
const arr = [1, 2, 3];
Array(1, 2, 3);

Question 5

Get 3rd to last index of an array

Answer 5

const arr = [1, 2, 3, 4, 5, 6];

console.log(arr.at(-3)];

Question 6

combine 2 arrays. returning new array and without returning new array

Answer 6

const arr1 = [a, b, c];
const arr2 = [1, 2, 3];

arr1.concat(arr2);

[…ar1, …arr2];

[].concat(arr1, arr2);

arr1.push(…arr2);

Question 7

Fill an array with values

Answer 7

fill(value)
fill(value, start)
fill(value, start, end)

Question 8

conditional to see if every element of an array passes

Answer 8

[12, 54, 18, 130, 44].every(x => x >= 10); // true

Question 9

find last element or index of an array given a testing function

Answer 9

array. findLast(…)

array. findLastIndex(…)

Question 10

const arr2 = [0, 1, 2, [[[3, 4]]]]
how to turn that into [0, 1, 2, 3, 4]

how to turn that flat with a function to apply to every element?

Answer 10

with flat
console.log(arr2.flat(2));

with “flatMap”

Question 11

determine whether the array contains a value.

Answer 11

[1, 2, 3].includes[1];

Question 12

the last index of an element

Answer 12

[1, 2, 3, 2].lastIndexOf(2)

Question 13

join all elements of an array to a string. also with a separator character

Answer 13

[1, 2, 3].join(‘-‘);

[1, 2, 3].toString(); // without separator

Question 14

remove first element of array

Answer 14

[1, 2, 3].shift();

Question 15

add to front of the array

Answer 15

array1.unshift(4, 5); // also returns length of new array

Question 16

find out if at least one element in the array satisfies a given function

Answer 16

[1, 2, 3].some(num => num < 4);

Question 17

return a portion of an array.

Answer 17

[1, 2, 3, 4, 5].slice(1, 3); // [2, 3]

Question 18

give splice parameters and what does it return

Answer 18

splice(start, deleteCount, itemToAdd)

returns the array of what was removed