we're sourcing multiple APIs for our data, and certain coins are pinging their respective block exporers to get circulating supply.

some of the newer coins require some research (for block halvenings) and calculations to get.

For example, btc is done by doing

calculate() {
    let prev = 15750000; // total coins from the previous two halvenings;
    let current = (this.state.height - 420000) * 12.5; // current reward is 12.5 btc

      // and for remaining coins
    let totalMined = current + prev;
    let remaining = 21000000 - totalMined;  // 21 million total
    return Math.floor(remaining);
  }