let ether = 0;
let token = 1;
let rate = 500000;

function buy(amount) {
    ether += amount;
    let tokensToMint = calc(amount);
    token += tokensToMint;
    console.log(token);
}

function calc(amount) {
    // return token * (1 + amount) / ether ^ (rate - 1);
    return token * ((1 + amount / ether) ** (rate / 1000000) - 1)
}

for (let i = 0; i < 10; i++) {
    buy(10);
}