Array by percentage of the previous value

I have an array of strings, amount and a percentage.

Every key is found in the object.
Its value is equal to the previous value plus the percentage.

This is the code I wrote:

const keys = ['a', 'b', 'c'];
const amount = 300;
const precentage = 0.5;
const obj = {};
let prevAmount = amount;
for (let i = 0; i < keys.length; i++) {
   if (i !== 0) {
     obj[keys[i]] = prevAmount + prevAmount * precentage;
     prevAmount = prevAmount + prevAmount * precentage;
   } else {
     obj[keys[i]] = amount;
     prevAmount = amount;
   }
}

The obj is:

{a: 300, b: 450, c: 675}

I don’t like this code. It looks too long for me.

Is there a way to make it more readable and short?

>Solution :

You can simply track the previous amount and update it on each iteration.

const keys = ['a', 'b', 'c'];
const amount = 300;
const percentage = 0.5;

const result = {};

let prev = amount;
for (const key of keys) {
  result[key] = prev;
  prev = prev + (prev * percentage);
}

console.log(result)