programming

虛擬貓咪原始碼＆智慧合約入門筆記

發表迴響

最近想多了解智慧合約的實際應用狀況，希望能跟區塊鏈上的智慧合約做簡單互動。

於是找了目前最成功的應用之一「虛擬貓咪」來研究。

分享一下目前的研究心得。

在開始之前，可以先閱讀以下兩個連結，對於閱讀本文會非常有幫助：

https://medium.com/loom-network/how-to-code-your-own-cryptokitties-style-game-on-ethereum-7c8ac86a4eb3

https://medium.com/loom-network/your-crypto-kitty-isnt-forever-why-dapps-aren-t-as-decentralized-as-you-think-871d6acfea

智慧合約不是完全公開透明的

以虛擬貓咪為例，智慧合約本身看似可以在此取得：

https://etherscan.io/address/0x06012c8cf97bead5deae237070f9587f8e7a266d#code

但貓咪基因科學的合約是額外佈署的，不但可以由作者動態修改，而且還只有 opcode 可讀。

同樣的道理，您也可以利用這種「設定外部合約」並且不公佈那份外部合約的 Solidity 原始碼，來達成這種保密效果，還讓合約保持可以更新、升級的空間。

智慧合約不是完全去中心化的

除此之外，虛擬貓咪智慧合約定義了 CEO、CFO、COO 三個管理員角色。這三個角色各自有額外權力，甚至可以凍結整個合約的運行。

不僅如此，區塊鏈上的資料看似永恆，但其實除了原始團隊，沒人可以解讀基因編碼。因此一大部份 value 還是來自傳統 web server。所以虛擬貓咪根本沒辦法脫離作者團隊獨立存活。

如何用 web3.js 讀取 address balance？以我與虛擬貓咪為例

要讀取每個地址的以太幣餘額，最簡單的方式就是直接透過 etherscan.io

比如說，我的個人餘額可以在此查看：https://etherscan.io/address/0xcb0418eae76e14c214d79b8305ca34669075cba6

而虛擬貓咪這份合約地址的餘額，可以在此查看：https://etherscan.io/address/0x06012c8cf97bead5deae237070f9587f8e7a266d

以工程師的立場，會希望用程式去跟區塊鏈互動。以在網頁內使用 web3.js 為例，安裝了 MetaMask 來連線到區塊鏈之後，可以用以下程式碼讀取地址餘額：

  var web3Provider = web3.currentProvider;

  var web3 = new Web3(web3Provider);

  var tonyAddress = '0xcb0418eae76e14c214d79b8305ca34669075cba6';

  var cryptoKittiesContractAddress = '0x06012c8cf97bead5deae237070f9587f8e7a266d';

  web3.eth.getBalance(tonyAddress, function(error, result){
    console.log('tony balance: ' + result);
  });

  web3.eth.getBalance(cryptoKittiesContractAddress, function(error, result){
    console.log('crypto kitties balance: ' + result);
  });

如何用 web3.js 讀取智慧合約的 public variable？以虛擬貓咪為例

試著讀取智慧合約中三個公開變數的值。最簡單的方式一樣是透過 etherscan.io

可以在這裡看到三個管理員（CEO、COO、CFO）的地址： https://etherscan.io/address/0x06012c8cf97bead5deae237070f9587f8e7a266d#readContract

用 web3.js 來讀取的話，可以先去 etherscan.io 取得合約的 ABI：

https://etherscan.io/address/0x06012c8cf97bead5deae237070f9587f8e7a266d#code

接著像這樣從區塊鏈上讀出值：

  var web3Provider = web3.currentProvider;

  var web3 = new Web3(web3Provider);

  var cryptoKittiesContractAddress = '0x06012c8cf97bead5deae237070f9587f8e7a266d';

  var AbiOfContract = 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},{"name":"_owner","type":"address"}],"name":"createPromoKitty","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"secs","type":"uint256"}],"name":"setSecondsPerBlock","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"paused","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[],"name":"withdrawBalance","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"_tokenId","type":"uint256"}],"name":"ownerOf","outputs":[{"name":"owner","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"GEN0_CREATION_LIMIT","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"newContractAddress","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_address","type":"address"}],"name":"setSaleAuctionAddress","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"_owner","type":"address"}],"name":"balanceOf","outputs":[{"name":"count","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_v2Address","type":"address"}],"name":"setNewAddress","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"secondsPerBlock","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[],"name":"pause","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"_owner","type":"address"}],"name":"tokensOfOwner","outputs":[{"name":"ownerTokens","type":"uint256[]"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_matronId","type":"uint256"}],"name":"giveBirth","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[],"name":"withdrawAuctionBalances","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"symbol","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"","type":"uint256"}],"name":"cooldowns","outputs":[{"name":"","type":"uint32"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"","type":"uint256"}],"name":"kittyIndexToOwner","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_to","type":"address"},{"name":"_tokenId","type":"uint256"}],"name":"transfer","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"cooAddress","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"autoBirthFee","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"erc721Metadata","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_genes","type":"uint256"}],"name":"createGen0Auction","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"_kittyId","type":"uint256"}],"name":"isReadyToBreed","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"PROMO_CREATION_LIMIT","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_contractAddress","type":"address"}],"name":"setMetadataAddress","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"saleAuction","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"_id","type":"uint256"}],"name":"getKitty","outputs":[{"name":"isGestating","type":"bool"},{"name":"isReady","type":"bool"},{"name":"cooldownIndex","type":"uint256"},{"name":"nextActionAt","type":"uint256"},{"name":"siringWithId","type":"uint256"},{"name":"birthTime","type":"uint256"},{"name":"matronId","type":"uint256"},{"name":"sireId","type":"uint256"},{"name":"generation","type":"uint256"},{"name":"genes","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_sireId","type":"uint256"},{"name":"_matronId","type":"uint256"}],"name":"bidOnSiringAuction","outputs":[],"payable":true,"stateMutability":"payable","type":"function"},{"constant":true,"inputs":[],"name":"gen0CreatedCount","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"geneScience","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_matronId","type":"uint256"},{"name":"_sireId","type":"uint256"}],"name":"breedWithAuto","outputs":[],"payable":true,"stateMutability":"payable","type":"function"},{"inputs":[],"payable":false,"stateMutability":"nonpayable","type":"constructor"},{"payable":true,"stateMutability":"payable","type":"fallback"},{"anonymous":false,"inputs":[{"indexed":false,"name":"owner","type":"address"},{"indexed":false,"name":"matronId","type":"uint256"},{"indexed":false,"name":"sireId","type":"uint256"},{"indexed":false,"name":"cooldownEndBlock","type":"uint256"}],"name":"Pregnant","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"name":"from","type":"address"},{"indexed":false,"name":"to","type":"address"},{"indexed":false,"name":"tokenId","type":"uint256"}],"name":"Transfer","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"name":"owner","type":"address"},{"indexed":false,"name":"approved","type":"address"},{"indexed":false,"name":"tokenId","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"name":"owner","type":"address"},{"indexed":false,"name":"kittyId","type":"uint256"},{"indexed":false,"name":"matronId","type":"uint256"},{"indexed":false,"name":"sireId","type":"uint256"},{"indexed":false,"name":"genes","type":"uint256"}],"name":"Birth","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"name":"newContract","type":"address"}],"name":"ContractUpgrade","type":"event"}];

  var contractAbi = web3.eth.contract(AbiOfContract);

  var myContract = contractAbi.at(cryptoKittiesContractAddress);

  myContract.ceoAddress(function(error, result){
    console.log('ceo address: ' + result);
  });

  myContract.cooAddress(function(error, result){
    console.log('coo address: ' + result);
  });

  myContract.cfoAddress(function(error, result){
    console.log('cfo address: ' + result);
  });

如何用 web3.js 呼叫智慧合約的 public function？以虛擬貓咪為例

呼叫公開函式的話，最簡單的方法是透過 etherscan.io。

以虛擬貓咪的 getKitty 函式為例，如果要找出 ID 為 1 的那隻創世貓咪的資料，只要在欄位內輸入送出即可：

https://etherscan.io/address/0x06012c8cf97bead5deae237070f9587f8e7a266d#readContract

用 web3.js 來讀取的話，則可以像這樣來呼叫函式（以分別抓出1、2、3 三隻貓咪為例）：

  var web3Provider = web3.currentProvider;

  var web3 = new Web3(web3Provider);

  var cryptoKittiesContractAddress = '0x06012c8cf97bead5deae237070f9587f8e7a266d';

  var AbiOfContract = [{"constant":true,"inputs":[{"name":"_interfaceID","type":"bytes4"}],"name":"supportsInterface","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"cfoAddress","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"_tokenId","type":"uint256"},{"name":"_preferredTransport","type":"string"}],"name":"tokenMetadata","outputs":[{"name":"infoUrl","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"promoCreatedCount","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"name","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_to","type":"address"},{"name":"_tokenId","type":"uint256"}],"name":"approve","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"ceoAddress","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"GEN0_STARTING_PRICE","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_address","type":"address"}],"name":"setSiringAuctionAddress","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"totalSupply","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"pregnantKitties","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"_kittyId","type":"uint256"}],"name":"isPregnant","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"GEN0_AUCTION_DURATION","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"siringAuction","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_from","type":"address"},{"name":"_to","type":"address"},{"name":"_tokenId","type":"uint256"}],"name":"transferFrom","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"_address","type":"address"}],"name":"setGeneScienceAddress","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"_newCEO","type":"address"}],"name":"setCEO","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"_newCOO","type":"address"}],"name":"setCOO","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"_kittyId","type":"uint256"},{"name":"_startingPrice","type":"uint256"},{"name":"_endingPrice","type":"uint256"},{"name":"_duration","type":"uint256"}],"name":"createSaleAuction","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[],"name":"unpause","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"","type":"uint256"}],"name":"sireAllowedToAddress","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"_matronId","type":"uint256"},{"name":"_sireId","type":"uint256"}],"name":"canBreedWith","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"","type":"uint256"}],"name":"kittyIndexToApproved","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_kittyId","type":"uint256"},{"name":"_startingPrice","type":"uint256"},{"name":"_endingPrice","type":"uint256"},{"name":"_duration","type":"uint256"}],"name":"createSiringAuction","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"val","type":"uint256"}],"name":"setAutoBirthFee","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"_addr","type":"address"},{"name":"_sireId","type":"uint256"}],"name":"approveSiring","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"_newCFO","type":"address"}],"name":"setCFO","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"_genes","type":"uint256"},{"name":"_owner","type":"address"}],"name":"createPromoKitty","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[{"name":"secs","type":"uint256"}],"name":"setSecondsPerBlock","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"paused","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[],"name":"withdrawBalance","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"_tokenId","type":"uint256"}],"name":"ownerOf","outputs":[{"name":"owner","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"GEN0_CREATION_LIMIT","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"newContractAddress","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_address","type":"address"}],"name":"setSaleAuctionAddress","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"_owner","type":"address"}],"name":"balanceOf","outputs":[{"name":"count","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_v2Address","type":"address"}],"name":"setNewAddress","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"secondsPerBlock","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[],"name":"pause","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"_owner","type":"address"}],"name":"tokensOfOwner","outputs":[{"name":"ownerTokens","type":"uint256[]"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_matronId","type":"uint256"}],"name":"giveBirth","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":false,"inputs":[],"name":"withdrawAuctionBalances","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"symbol","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"","type":"uint256"}],"name":"cooldowns","outputs":[{"name":"","type":"uint32"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"","type":"uint256"}],"name":"kittyIndexToOwner","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_to","type":"address"},{"name":"_tokenId","type":"uint256"}],"name":"transfer","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"cooAddress","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"autoBirthFee","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"erc721Metadata","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_genes","type":"uint256"}],"name":"createGen0Auction","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[{"name":"_kittyId","type":"uint256"}],"name":"isReadyToBreed","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"PROMO_CREATION_LIMIT","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_contractAddress","type":"address"}],"name":"setMetadataAddress","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"},{"constant":true,"inputs":[],"name":"saleAuction","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[{"name":"_id","type":"uint256"}],"name":"getKitty","outputs":[{"name":"isGestating","type":"bool"},{"name":"isReady","type":"bool"},{"name":"cooldownIndex","type":"uint256"},{"name":"nextActionAt","type":"uint256"},{"name":"siringWithId","type":"uint256"},{"name":"birthTime","type":"uint256"},{"name":"matronId","type":"uint256"},{"name":"sireId","type":"uint256"},{"name":"generation","type":"uint256"},{"name":"genes","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_sireId","type":"uint256"},{"name":"_matronId","type":"uint256"}],"name":"bidOnSiringAuction","outputs":[],"payable":true,"stateMutability":"payable","type":"function"},{"constant":true,"inputs":[],"name":"gen0CreatedCount","outputs":[{"name":"","type":"uint256"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":true,"inputs":[],"name":"geneScience","outputs":[{"name":"","type":"address"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_matronId","type":"uint256"},{"name":"_sireId","type":"uint256"}],"name":"breedWithAuto","outputs":[],"payable":true,"stateMutability":"payable","type":"function"},{"inputs":[],"payable":false,"stateMutability":"nonpayable","type":"constructor"},{"payable":true,"stateMutability":"payable","type":"fallback"},{"anonymous":false,"inputs":[{"indexed":false,"name":"owner","type":"address"},{"indexed":false,"name":"matronId","type":"uint256"},{"indexed":false,"name":"sireId","type":"uint256"},{"indexed":false,"name":"cooldownEndBlock","type":"uint256"}],"name":"Pregnant","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"name":"from","type":"address"},{"indexed":false,"name":"to","type":"address"},{"indexed":false,"name":"tokenId","type":"uint256"}],"name":"Transfer","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"name":"owner","type":"address"},{"indexed":false,"name":"approved","type":"address"},{"indexed":false,"name":"tokenId","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"name":"owner","type":"address"},{"indexed":false,"name":"kittyId","type":"uint256"},{"indexed":false,"name":"matronId","type":"uint256"},{"indexed":false,"name":"sireId","type":"uint256"},{"indexed":false,"name":"genes","type":"uint256"}],"name":"Birth","type":"event"},{"anonymous":false,"inputs":[{"indexed":false,"name":"newContract","type":"address"}],"name":"ContractUpgrade","type":"event"}];

  var contractAbi = web3.eth.contract(AbiOfContract);
  var myContract = contractAbi.at(cryptoKittiesContractAddress);

  myContract.getKitty(1, function(error, result){
    console.log('kitty info: ' + result);
  });

  myContract.getKitty(2, function(error, result){
    console.log('kitty info: ' + result);
  });

  myContract.getKitty(3, function(error, result){
    console.log('kitty info: ' + result);
  });

心得感想

像這樣的智慧合約，究竟有多少應用場景？

一個 dapp 該去中心化到什麼程度？智慧合約的未來到底有多少潛力？實在沒人有把握。

還是老話一句，建議有心參與的朋友，保持懷疑精神，花時間了解更多，建立自己的觀點跟看法，不要輕信任何人的說法。

（完）

programming, 工作

Ethereum 智慧合約佈署初體驗：數據與成本分享

發表迴響

正式佈署一份智慧合約是什麼感覺？

它的佈署速度、佈署成本又是多少呢？

我親自跑了一次流程。分享一下實際的數據與心得。

發行個人專屬加密貨幣：阿川幣

我直接拿官網的範例程式碼來修改參數，發行阿川幣：

https://ethereum.org/token

官網提供兩份範本，一份只有基本功能，一份具備進階功能。

以太錢包預估了基本合約的佈署成本是 0.000715604 ether（約合新台幣 22 元）：

erc20

而進階合約的佈署成本是 0.001010363 ether（約合新台幣 31 元）：

advanced

我選擇佈署基本合約就好。輸入參數之後，會發現成本微幅提昇到 0.000777146 ether（約合新台幣 24 元）：

with-parameters

按下 DEPLOY 按鈕，會確認密碼，並顯示預估成本 0.000777146 ether 是因為預估耗用 777,146 gas，並且多準備 0.0001 ether 作為緩衝：

gas-usage

送出後，以太錢包會顯示 etherscan.io 網站上的交易連結：

https://etherscan.io/tx/0xcedd9b10deb6ca64b44a547244045383d4563f916849c005308453d939f69c51

大約 6 分鐘後，網頁上的交易狀態顯示為 success：

6-min-success

不過以太錢包內還沒有同步顯示完成。再過 4 分鐘，也就是大約 10 分鐘後，以太錢包上才顯示 created：

10-min-success

進入帳號底下查看，會看到 2,100 萬枚阿川幣正確顯示，代表合約佈署完成了。

我本來有 0.01 ether，現在剩 0.009222854 ether，所以的確是被扣款 0.000777146 ether，以太錢包的預估成本是準確的：

final-balance

並且可以查看合約的地址，合約的原始碼也在裡面：

https://etherscan.io/address/0x03f6a68baf85840a513a71f49f5f8fb1edcf27f6

心得感想

這次初體驗，以個人用戶來說，我認為佈署速度不算太慢（約 6 – 10 分鐘），手續費也還行（約合新台幣 24 元），都還 OK。

所以佈署這種範例程式碼等級的合約，不困難，也不昂貴。

可以以此為基礎，再進一步研發更複雜的智慧合約。

至於智慧合約的未來到底有多少潛力？其實沒人有把握。

還是建議有心參與的朋友，保持懷疑精神，建立自己的觀點跟看法，不要輕信任何人的說法。

（完）

公眾議題, 工作

以太幣購買與傳送初體驗：數據與心得分享

發表迴響

購買與轉帳加密貨幣，究竟是什麼感覺？

它的交易速度、交易成本又是多少呢？

我親自跑了一次流程。分享一下實際的數據與心得。

在 MaiCoin 註冊帳號

我選擇的加密貨幣是以太幣。

台灣能購買以太幣的管道不多，查詢之後決定使用 MaiCoin 的服務，因為可以在萊爾富繳費。

https://www.maicoin.com/

原本只想買個新台幣 300 元，但發現 MaiCoin 規定單次購買至少要滿 0.05 枚以太幣，當下約合新台幣 1,806 元。

所以我用這數字下單了，確認後取得了萊爾富的繳費代碼。

因為匯率波動太大，MaiCoin 提醒我要在 15 分鐘內繳費，否則可能以新匯率計價。

在萊爾富使用代碼繳費

我到萊爾富時已經超過 15 分鐘了，使用 Life-ET 代碼繳費，萊爾富收取手續費 20 元，總計支出 1,826 元，繳費完成。

在 MaiCoin 確認交易完成

回家打開 MaiCoin 網站，馬上確認了繳費完畢，並顯示我帳號擁有 0.04984127 枚以太幣。因為匯率變動，我受到了小小損失。

111

使用 Ethereum Wallet 建立帳號（address）

MaiCoin 上的以太幣是記在 MaiCoin 底下，為了建立一個正式的以太坊地址，我使用了官方的 Ethereum Wallet 建立帳號，並取得地址。

從 MaiCoin 傳送以太幣到我的 address

MaiCoin 規定傳送的以太幣數量至少為 0.01。

確認之後，明細會顯示處理中。

222

在 etherchain.org 確認交易內容

MaiCoin 約 11 分鐘後通知我，確認交易完成。

我電腦上的 Ethereum Wallet 需要下載完所有區塊鏈資料（目前約為 55.1 GB！），才能顯示我的帳戶餘額。

不想等這麼多資料下載完，所以我去 etherchain.org 上確認區塊鏈內容。

區塊編號  4992415 ，實際交易時間約為 9 分鐘。

https://www.etherchain.org/tx/0x37f3597ee17754494ba88e732f6ff32ed604b18fac9e786071089ea773d39501

交易內容 0.01 ETH ，約合美金 $12.31。

交易手續費 0.00084 ETH，約合美金 $1.03，這費用是由 MaiCoin 支付，沒有扣到我身上。

55 GB 資料下載完後，我也在錢包上看到了餘額 0.01 ETHER 沒有錯。

333

心得感想

這次初體驗，以個人用戶來說，我認為交易速度不算太慢，還 OK，手續費也還行。

但是作為投資則非常困難，除了手續費之外，在 MaiCoin 上的匯率跟國外交易所的匯率也有差別。

整體說起來，想到這段金融過程，幾乎沒有銀行或是政府機構介入，而是由全世界各地的電腦一起完成，確實感覺區塊鏈科技滿酷的。

但許多 ICO 相關詐騙、根本沒用的區塊鏈假應用、三不五時傳出的交易所危機等等，讓人不得不保持戒心。

建議有心參與的朋友，以學術精神，保持懷疑，勇於懷疑，建立自己的觀點跟看法，不要輕信任何人的說法。

（完）

programming, 工作

搞懂為何設定 React、JSX、ES2015、Babel、Webpack 的學習筆記

發表迴響

學習 React、JSX、ES2015、Babel、Webpack 等等現代化的前端開發觀念時，會需要安裝很多工具、設定多個檔案、用到許多指令。

大部份教學文章只講「怎麼設定這些」而沒說明「為何要設定這些」。照著做完感覺很不放心。

最近我試著搞懂「為何要設定這些」，跟大家分享一下這個逐步搞懂的過程。

前言

這篇文章假設你想要開始用 React 開發，希望搞懂相關的前端環境與設定。

如果你想知道用 React 到底有什麼好處，可以參閱以下連結：

Introducing JSX、Thinking in React、簡單聊一下 ONE-WAY DATA FLOW、TWO-WAY DATA BINDING 與前端框架

接下來，這篇文章會以試著寫一個陽春的 App 元件作為範例，內含 ChildA 跟 ChildB 兩個元件。

讓我們開始吧！

第一步：直接在 html 檔內開發 React 給瀏覽器執行

我們先用原始的開發方法硬搞看看！

用 script 標籤直接從 CDN 引入 react.js 跟 react-dom.js 檔案。

然後試著寫一個陽春的 App 元件，內含 ChildA 跟 ChildB 兩個元件。

這個 html 檔內容會像這樣：








    Should Render Here

source code

結果瀏覽器無法執行 React 相關的程式碼！

原因有兩個：

1. 瀏覽器看不懂 ES2015 的語法（class、extends）

2. 瀏覽器看不懂那個像是把 html 寫在 js 裡面的 JSX 語法

該怎麼辦呢？

第二步：用 Babel 讓瀏覽器能看懂 ES2015 與 JSX 語法

我們可以使用 Babel 套件來來編譯 ES2015 與 JSX 的程式碼，讓瀏覽器能夠看懂。

只要在 html 內加上這行：

然後在要編譯的 script 加上 type=’text/babel’ 即可：










    Should Render Here

source code

然而，這樣做卻又產生3個新的問題：

1. 有N個檔案，就要打編譯指令N次，太累了

2. 透過 script 標籤引入N個檔案，會增加伺服器負擔、也會增加用戶端等待時間

3. babel 相關的程式碼都移出瀏覽器了，react.js 跟 react-dom.js 卻還是在瀏覽器內引入

第一個問題還算簡單，可以改成輸入指定資料夾的指令，就可一次編譯：

./node_modules/.bin/babel src/ -d dist/ --presets es2015,react

但是第二三個問題就棘手得多。

有鑑於此，需要找方法一次解決這三個問題：設法一口氣全部編譯、封裝成單一檔案、並且函式庫統一用NPM在伺服器端安裝與管理吧！

第四步：使用 webpack 來解決這些整合問題

webpack 會利用 babel-loader 套件來呼叫核心的 babel-core，所以先分別安裝它們：

npm install --save-dev babel-core

npm install --save-dev babel-loader

npm install --save-dev webpack

我們不會透過命令列去使用 babel 了，既然用不到就先把它移除吧：

npm uninstall babel-cli

我們也不會用 script 標籤引入 react.js 跟 react-dom.js 檔案了。一口氣全部編譯時會用到，所以用NPM安裝它吧：

npm install --save-dev react

npm install --save-dev react-dom

前面說過 babel 版本 6 以後預設不支援 ES2015 與 JSX，現在不透過命令列設定 presets 的話，就需要建立 .babelrc 檔案去開啟支援：

{
  "presets": ["es2015", "react"]
}

然後為了讓 webpack 在一口氣全部編譯成一個檔案時，能看懂檔案跟套件之間的相依性，因此需要按照 ES2015 的 import/export 語法寫清楚。

例如原本的 App.jsx 就要改寫成這樣：

import React from 'react';
import ChildA from './ChildA.jsx';
import ChildB from './ChildB.jsx';

export default class App extends React.Component {
  render() {
    return (
      

        
Hello App!

        
        
      

    );
  }
}

src 資料夾內的檔案都要進行改寫。

最後建立 webpack.config.js 來設定檔案路徑，並指定使用 babel-loader 來幫忙編譯：

var path = require('path');

module.exports = {
  module: {
    loaders: [{
      loader: 'babel-loader',
    }]
  },
  entry: './src/index.jsx',
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, './dist/')
  }
}

就可以透過命令列執行 webpack了：

./node_modules/.bin/webpack

這段指令有點長，可以把它放進 package.json 的 scripts 欄位：

  "scripts": {
    "build": "webpack"
  },

之後就可以用下列指令來進行編譯工作了：

npm run build

會得到我們要的結果：一個檔案搞定一切！


    Should Render Here

source code

大功告成！終於搞定我們想要的所有效果！

結語

本篇文章提到的內容，根據不同的套件版本，實務上有多種方式去安裝、設定達到同樣效果。

但是核心觀念是共通的！

可以此為基礎，探索更多的現代前端開發方法，學習更多工具的功能與設定！

（完）

（Photo via 8 Kome, CC licensed.）

工作

Cafe Nomad 蒐集 1,700 間咖啡廳的理由

3 則迴響

我是一個很常去咖啡廳用筆電的軟體工程師。

每次在巷子內找到新的獨立小店時，我心中都會浮現3個念頭：

1. 又是一間精緻用心的獨立咖啡廳。這種店台北應該有幾百家，如果每間都去過，一定很有成就感

2. 這間店的位置真是太低調了，就算開幕滿一年，恐怕連附近住戶都不知道它的存在

3. 根據以上兩點，好像可以推論：巷子內的這些咖啡廳，普遍被埋沒了

2016年11月，趁著離職之後時間多，我決定驗證一下這些直覺。

我把過去幾年去過的20多間咖啡廳資料整理出來，根據自己最在乎的7個指標做了評分，接著上網再找出台北60間咖啡廳的店名，作成 Google 試算表，等待網友幫忙評分。

把這個試算表貼到批踢踢的軟體工程師看板之後：

[討論] 台北適合工作的咖啡廳

反應很不錯，隔天下午時，大部份咖啡廳都得到網友評分了，資料也被新增到100多間。

然後，我寫了程式把試算表的內容轉成網頁版的表格，接著訂購了一個網址：cafenomad.tw

稍微做了SEO與SMO之後，我把這張表格分享到我的一個粉絲專頁：

https://www.facebook.com/permalink.php?story_fbid=982000048579054&id=650279948417734

這則貼文隔天被分享了1,200次，再被轉分享之後，最後共計被分享了30,000次，當天有90,000人來看 Cafe Nomad：

1

這些流量也帶來更多人幫忙整理咖啡廳資料，最後台北收錄了200多間，其他地區也共計有200多間。

網友們的熱情參與，幾乎證明了巷子內的這些咖啡廳果然被埋沒了。

換句話說，台灣獨立咖啡廳產業的整體產值被低估了。

那麼，該如何提昇台灣獨立咖啡廳產業的整體產值呢？

我想到三個辦法：

1. 針對原本就會去獨立咖啡廳的族群：鼓勵他們更頻繁地消費
2. 針對只去連鎖咖啡廳的族群：邀請他們試試看獨立咖啡廳
3. 針對近年來與日俱增的國際觀光客：鼓勵他們去咖啡廳喝一杯

針對原本就會去獨立咖啡廳的族群

這是其中最簡單的方向。只要把這份清單給他們看就行了。

然後不斷開發更好用的找店功能，然後定期告訴他們有新功能就可以了。

這個族群也容易觸及：只要去批踢踢、Facebook社團貼文就可以了，大概像這樣：

[閒聊] 我做了一個蒐集956間咖啡廳資料的網站

[閒聊] 我做了一張台中咖啡廳地圖

[閒聊] 一口氣逛高雄全部咖啡廳的FB粉專的方法

[閒聊] 台南咖啡廳地圖：150間店 + 1,000張照片

https://www.facebook.com/groups/1507207486163325/permalink/1793163560901048/

這些貼文的反應都很不錯，也讓更多人知道巷弄小店要去哪裡找。

針對只去連鎖咖啡廳的族群

這是一個十分困難的方向，但還是有出力空間。

時不時會有咖啡產業的新聞出現，這種時候直接去人多的地方，然後跟大家談談自己對獨立咖啡廳的觀察跟心得就可以了。例如八卦版就很適合去po文：

Re: [問卦] 為什麼台北都很少小資本額的咖啡館？

把握住這種機會的話，可以吸引到至少50,000人開始想試試巷弄小店。

2

近年來與日俱增的國際觀光客

這是最困難的方向，光是要觸及這些旅客就很難，但還是有出力空間。

我把網站介面翻譯成了英文版：

https://cafenomad.tw/en

然後貼到幾個在台灣的英文社群網站：

https://www.reddit.com/r/taiwan/comments/5uw792/cafe_nomad_700_best_cafes_to_work_in_taiwan/

https://www.facebook.com/groups/357339197762790/permalink/723135624516477/

接著找 Cafe Nomad 社群的人幫忙翻譯成日文韓文版

https://cafenomad.tw/ja/

https://cafenomad.tw/ko/

然後再貼到相關的台日交流社團、台韓交流社團：

https://www.facebook.com/groups/japantaiwan/permalink/1392935974078433/

https://www.facebook.com/groups/partyintaiwan2/permalink/1453874974920063/

反應普遍很正面，雖然比較間接，但還是有點效果。

結語

網站上線5個月之後，我開始會在FB收到店家這樣的訊息：

3

Cafe Nomad 現在已經蒐集超過1,700間店、超過3,500筆評分、500則留言。每天都有超過1,000人主動上站尋找他下一間要去的巷弄小店。

最近替 Cafe Nomad 新增了店家贊助的功能，也找到了幾間贊助店家，所以我也得到了一些報酬。

在過去三年，我去這種巷弄小店消費了幾百次。整體說起來，在台灣，你很難找到一間會讓你失望的獨立咖啡廳。

花了很多時間做這網站，其實我也不太確定自己在幹嘛，但因為是滿有趣的事情，所以就算完全行不通，好像也沒關係。

我唯一確定的是，台灣這些巷弄小店，確實普遍被埋沒了。

附註：

「店家贊助」功能是我替 Cafe Nomad 最新加上去的廣告功能。

它會將咖啡廳的名稱與照片獨立顯示出來，並且在清單與地圖內特別呈現。

歡迎有興趣的店家點這裡看看這個贊助功能的細節！

（Photo via unsplash.com, licensed under Creative Commons Zero）

創業

我現在就想用你的產品，就算破破的也請馬上給我用

1 則迴響

「當你有一個創業點子的時候，問問自己：有誰現在就想要這個產品？有誰超級渴望這產品，即便是小團隊做出來的破爛版本、即便這團隊根本沒人聽過，他們也照樣想馬上使用？如果你無法回答這個問題，那這個創業點子恐怕不太妙。」── Paul Graham

每次聽到有人正打算要創業、分享點子，我腦中都會浮現上面那個 Paul Graham 提到的問題。

不妨用更尖銳的方式描述這個問題：「這東西有人要用嗎？誰？你認識或見過任何一位這樣的人嗎？你說得出那人的名字嗎？現在打電話給他介紹這產品，他會說：『我現在就想用你的產品，就算破破的也請馬上給我用』？」

這個問題乍看之下沒什麼，實際投身新創產業之後發現，它會在很早期就給你迎頭痛擊。

如果無法回答這問題，那把產品推出之後，要是沒什麼人用，就會心想：是我功能不夠豐富、是我介面不夠漂亮，那再改一下。

改完一下再一下，還是沒人用的話就再改一下。

再不然就是會心想：都是我廣告下得不夠多。

於是付點錢給Facebook、付點錢給Google，還是沒人用的話就再燒多點廣告錢。

如果你自己都不知道這產品是誰會馬上想用，那就幾乎一定會陷入上述的挫折感循環，永無止盡投入的陷阱。

毫無正向回饋的不斷付出，會讓人感到焦慮、靈感枯竭，覺得自己像是跑步機上面的老鼠，沒有目的地疲憊奔跑著，卻也真的只是在跑而已。

在搞定了上述第一個問題之後，還可以參考 Paul 提供的另一個建議：

「相較於讓一堆人普通滿意，還不如讓少數人非常滿意比較好。」── Paul Buchheit & Paul Graham

然後你就會針對很明確的一小群人，非常專注地打造產品給他們。

這些建議之所以那麼多人沒注意到，是因為它們非常違反直覺。

它們乍看之下似乎是在劃地自限、從一開始就把東西做很小、從一開始就把市場弄很小。

實際上並非如此，它們只是一種讓自己能在一開始就保持專注的方法。可以接著把產品越做越大。

「擴展市場大小比提升用戶滿意度簡單。更重要的恐怕是，你比較難欺騙自己。如果你自認產品品質已經85分了，你怎知道它不是70分？說不定只有10分？但是你很容易就知道產品有多少用戶。」── Paul Graham

產品即使一開始只讓一小群人愛不釋手，但使命仍然可以定的很巨大。努力往那裡走就是了。

就算是一邊做一邊確立使命感，都好過於一開始就好高騖遠。

而且這種作法會大幅提昇產品上線速度、新功能上線速度。

愛情裡有一個關於緣份的描述：「世界上有一個人，每天每天都在想，要是有一天，能有像你這樣的人出現，那該有多好。」

不妨直接拿來當作創業的比喻：「世界上有一些人，每天每天都在想，要是有一天，能有像你做的這樣的產品出現，那該有多好。」

她當然知道你不完美，她當然知道你一定有缺點，但是她見到你的瞬間就已經決定包容你的一切。

有些人正在等你介紹你的產品，然後他們會對你說：我現在就想用你的產品，就算破破的也請馬上給我用。

創業

創業：退後100步的做法

2 則迴響

會選擇創業的人，大概都是對某種現況感到不滿，想要改變那現況，所以才創業。

「我要改變世界！當一個有影響力的人！在宇宙間留下點什麼！」他們會這麼說。

有趣的是，要改變現況、影響別人，事實上不需要下定決心創業、不需要負債百萬、不需要籌備一年半載。

你今天下午就可以穿上鞋子出門，然後改變現況、影響別人。

這兩者的差別在於：你多大程度上改變了現況？你影響了多少人？

讓我們隨便舉個小明想要創業的例子。

小明最近發現海灘上常常有很多垃圾，於是他想到了一個網路創業的點子：成立一個「能與網友一起淨灘的社群網站」。

它是一個社交網站，你能邀請感興趣的網友週末一起去淨攤，在做環保的同時，還能交到知心朋友、找到男女朋友。

商業模式呢？嗯，小明心想，創業做大之後就是大，隨便弄都能賺到錢。把淨攤蒐集到的垃圾統一分類，做資源回收賣掉，數量一大就發財了。做環保的同時還能交友，多棒！不然跟會員收取會員月租費或是年費吧！人夠多也是發財了。

小明的社群網站上線之後大概沒什麼人註冊，創業幾個月都沒有網友相約去淨攤，更不用說向使用者收費了。

小明創業幾個月之後發現這點子不可行，於是把網站收掉了。

小明沒想到退後100步的做法。

同樣喜歡淨灘的小華不同。

小華對於海灘污染的問題感到非常痛苦，他第一次看到骯髒的海灘就決心要改變了。

小華每個週末都會帶著垃圾袋，開車幾小時到海邊去撿垃圾。撿了幾年之後，他會邀請身邊的朋友一起去，大部份的人會拒絕，但有些人會答應。

小華可能也有過「能與網友一起淨灘的社群網站」這樣的點子，但他是如此渴望改變海灘，他根本等不到網站寫出來，他今天下午就想動手改變海灘的現況。

「做一陣子再邀請朋友一起吧」小華這樣心想。

「做一陣子再去發傳單，找路人一起吧」小華這樣心想。

「做一陣子再上網號召，找網友一起吧」小華這樣心想。

小華選擇了退後100步的做法，然後他知道往前一步的做法，還有再往前一步的做法。

上面這個「淨攤交友兼賣資收與賺會員費的社群網站」是我隨便想的例子，看似很扯，但是在網路創業圈，到處都是類似這樣的例子。

它們都有一個共同點：上線之後沒什麼人要用。

這時候該怎麼辦呢？可以用退後10步的做法再試試嗎？還是失敗怎麼辦？退後100步如何？

事實上，創業圈的人們大都很聰明、很有想法與創意，要想出退後1步、10步、100步的做法並不難。

真正困難的地方在於：你願意嗎？

退後10步的做法會變成要幹一堆麻煩事，創業者要捲起袖子做一堆很像在打工的事，不規模化也賺不了多少錢。

退後100步的做法會變得很像在做慈善，很像在做社會運動，根本賺不到錢，完全就是勞心勞力在對世界、對別人付出，根本沒賺頭，而且一點都不酷。但是對現況、對別人，都有直接影響力。

不是說想改變現況嗎？為什麼規模小一點就不做了呢？為什麼無法立刻賺到錢就不做了呢？

然後你才發現，他們沒那麼想改變世界。他們的改變世界有先決條件：改變世界的同時，我要能發財才行。

改變世界的同時，還要看起來夠酷才行。

賺不了錢我就不改變世界了。不夠酷我就不改變世界了。

但是在創業的歷史上，從一開始就有利可圖、從一開始就很酷的例子根本少之又少。

幾乎總是要在挫折之後，退後個幾步再試才行。或是從一開始就從退幾步的地方開始做起。

卻也只有真正對改變某種現況有使命感的人才願意這麼做。

觀察一下那些組織社會運動的人，他們不會說「我要上網號召萬人上街！但沒有萬人答應的話，我就不上街了」。

他們對現況是如此憤怒，以致於無論有沒有人理他，他都要出發去高喊理念，他都要冒著風險去衝撞、去挑戰現況。

也只有當你這麼做的時候，才真的可能發揮影響力。

你正在創業嗎？你想改變什麼現況呢？你對和你一樣對現況不滿的潛在用戶發表什麼理念？你要推出什麼產品或是服務來幫助他們？

你對他們做出多少承諾？

為了解決問題，你願意退後10步嗎？

為了解決問題，你願意退後100步嗎？

by 阿川先生