Javascript : Create an array with sequential integer values

For creation of an array with sequential integer values lets

consider following code

Code:

const n=10

const arr1 = Array.from(Array(n).keys());

console.log(arr1)

Output:

[

0, 1, 2, 3, 4,

5, 6, 7, 8, 9

]

Explantion:

Lets break down statement

Array.from(Array(n).keys())

into its parts.

1) Array(n): Creates a new array with a length of n. This array initially

contains empty slots (sparse array), meaning it has n slots but no

defined elements.

2) .keys(): Accesses the keys (indices) of the array. This returns an

iterator that generates sequential integer keys starting from 0 up

to n - 1.

3) Array.from(...): Converts the iterator (keys) into an array. The

Array.from method takes an iterable or array-like object and creates a

new array from its elements or values. In this case, it converts the

iterator of keys into an array containing integers from 0 to n - 1.

Code:

const n=10

let arr2 = new Array(n).fill().map((_,index)=> index)

console.log(arr2)

Output:

[

0, 1, 2, 3, 4,

5, 6, 7, 8, 9

]

Explanation:

The code above creates a new array of length n, fills it with undefined

values, and then uses the map method to transform each element to its

index value.

Note:

Instead of statement

let arr2 = new Array(n).fill().map((_,index)=> index)

if we put

let arr2 = new Array(n).map((_,index)=> index)

we get output as [ <10 empty items> ].

Observation:

Consider following code.

Code:

const n=10

let iterator = Array(n).keys()

for(var m of iterator ){

console.log(m)

}

Output:

0

1

2

3

4

5

6

7

8

9

Explanation:

Array(n).keys() method to create an iterator for generating sequential

integer keys from 0 to n - 1, and then iterates through this iterator

using a for...of