总量不是固定数值，而是由衰减规则定义 Blockchain: What is Mining? - Damien Cosset https://www.damiencosset.com/blockchain-what-is-mining/

max-btc.js

// First 210 000 blocks reward
const start_reward = 50

// The reward is modified every 210000 blocks
const reward_interval = 210000

const max_btc = () => {
  // 50 BTC = 5000000000 Satoshis
  // Satoshis are the smallest denomination in bitcoin
  let current_reward = 50 * 10 ** 8
  let total_btc = 0
  while( current_reward > 0 ){
    total_btc += reward_interval * current_reward
    current_reward = current_reward / 2
  }

  return total_btc
}

console.log(`The maximum amount of BTC created will be ${max_btc()} Satoshis, or ${max_btc() / 10**8} BTC`)
// The maximum amount of BTC created will be 2100000000000000 Satoshis, or 21000000 BTC