How do i concat an array only when it's not undefined

Question

I need to add multiple arrays together depending on user's preference some array might appear empty, how do I make sure the array I'm about to concat is not empty

here is my failed code

const num1 = [12,67,100] 
const num2 = [] 
const num3 = [23,191, 58]
const num4 = [23,30]

const numbers = num1.concat(`num${Math.random() * 10}`)

Create a 2D array (an array of arrays) instead of trying to access variables dynamically. Also, it's unclear what you mean by selecting an based on *user's preference* when you're using `Math.random()` — adiga, Feb 24 '20 at 12:06
You can simply add check for Array.length, if length is > 0, then only add. — Sarvesh Mahajan, Feb 24 '20 at 12:07
Even if the array is empty it should not be an issue as `[1,2].concat([])` is same as `[1,2]` — palaѕн, Feb 24 '20 at 12:10

score 0 · Answer 1 · answered Feb 24 '20 at 12:29

Following this answer, converting to 2d array and convert it to a single flat array, seems like the preferred solution

const values = [ [12,67,100], [], [23,191, 58], [23,30] ]

const numbers = [].concat(...values)

console.log(`items count: ${numbers.length}`)

const randomNumbers = numbers.map(num => parseInt(num * Math.random()))

score 0 · Answer 2 · answered Feb 24 '20 at 13:26

0

There you go, easy to understand:

constant numbers;
int randomArray = `num${Math.random() * 10}`;

if (randomArray.length > 0)
{
    numbers = num1.concat(randomArray);
}

answered Feb 24 '20 at 13:26

feedy

1,035
3
16

score 0 · Accepted Answer · edited May 29 '20 at 17:54

0

const num1 = [12, 67, 100]
const num2 = []
const num3 = [23, 191, 58]
const num4 = [23, 30]

const check = `num${Math.random() * 10}`
const numbers = num1.concat(check && check)

console.log(numbers);

edited May 29 '20 at 17:54

double-beep

4,567
13
30
40

answered May 29 '20 at 14:20

How do i concat an array only when it's not undefined

3 Answers3