How to duplicate indexes in array with numbers of second array, resulting third array in JS

I have an array of products amount, and another array of products ID’s.

I’m trying to do something like this:

arrayOfAmount = [2,3,4]

arrayOfId = [1,2,3]

resulting the third array of ID’s:

arrayOfProducts = [1,1,2,2,2,3,3,3,3]

how can I do that?

thank you in advance!

>Solution :

You can try this:

let arrayOfAmount = [2,3,4]

let arrayOfId = [1,2,3]

console.log(arrayOfId.flatMap((x,i)=>Array(arrayOfAmount[i]).fill(x)))