现在正是停下来重新回顾一下代码的好时机，思考一下重构的进展。现在我有了两个代码文件。 ##### statement.js ``` import createStatementData from './createStatementData.js'; function statement (invoice, plays) { return renderPlainText(createStatementData(invoice, plays)); } function renderPlainText(data, plays) { let result = `Statement for ${data.customer}\n`; for (let perf of data.performances) { result += ` ${perf.play.name}: ${usd(perf.amount)} (${perf.audience} seats)\n`; } result += `Amount owed is ${usd(data.totalAmount)}\n`; result += `You earned ${data.totalVolumeCredits} credits\n`; return result; } function htmlStatement (invoice, plays) { return renderHtml(createStatementData(invoice, plays)); } function renderHtml (data) { let result = `<h1>Statement for ${data.customer}</h1>\n`; result += "<table>\n"; result += "<tr><th>play</th><th>seats</th><th>cost</th></tr>"; for (let perf of data.performances) { result += ` <tr><td>${perf.play.name}</td><td>${perf.audience}</td>`; result += `<td>${usd(perf.amount)}</td></tr>\n`; } result += "</table>\n"; result += `<p>Amount owed is <em>${usd(data.totalAmount)}</em></p>\n`; result += `<p>You earned <em>${data.totalVolumeCredits}</em> credits</p>\n`; return result; } function usd(aNumber) { return new Intl.NumberFormat("en-US", { style: "currency", currency: "USD", minimumFractionDigits: 2 }).format(aNumber/100); } ``` ##### createStatementData.js ``` export default function createStatementData(invoice, plays) { const result = {}; result.customer = invoice.customer; result.performances = invoice.performances.map(enrichPerformance); result.totalAmount = totalAmount(result); result.totalVolumeCredits = totalVolumeCredits(result); return result; function enrichPerformance(aPerformance) { const result = Object.assign({}, aPerformance); result.play = playFor(result); result.amount = amountFor(result); result.volumeCredits = volumeCreditsFor(result); return result; } function playFor(aPerformance) { return plays[aPerformance.playID] } function amountFor(aPerformance) { let result = 0; switch (aPerformance.play.type) { case "tragedy": result = 40000; if (aPerformance.audience > 30) { result += 1000 * (aPerformance.audience - 30); } break; case "comedy": result = 30000; if (aPerformance.audience > 20) { result += 10000 + 500 * (aPerformance.audience - 20); } result += 300 * aPerformance.audience; break; default: throw new Error(`unknown type: ${aPerformance.play.type}`); } return result; } function volumeCreditsFor(aPerformance) { let result = 0; result += Math.max(aPerformance.audience - 30, 0); if ("comedy" === aPerformance.play.type) result += Math.floor(aPerformance.audience / 5); return result; } function totalAmount(data) { return data.performances .reduce((total, p) => total + p.amount, 0); } function totalVolumeCredits(data) { return data.performances .reduce((total, p) => total + p.volumeCredits, 0); } ``` 代码行数由我开始重构时的44行增加到了70行（不算`htmlStatement`），这主要是将代码抽取到函数里带来的额外包装成本。虽然代码的行数增加了，但重构也带来了代码可读性的提高。额外的包装将混杂的逻辑分解成可辨别的部分，分离了详单的计算逻辑与样式。这种模块化使我更容易辨别代码的不同部分，了解它们的协作关系。虽说言以简为贵，但可演化的软件却以明确为贵。通过增强代码的模块化，我可以轻易地添加HTML版本的代码，而无须重复计算部分的逻辑。 >  编程时，需要遵循营地法则：保证你离开时的代码库一定比来时更健康。 其实打印逻辑还可以进一步简化，但当前的代码也够用了。我经常需要在所有可做的重构与添加新特性之间寻找平衡。在当今业界，大多数人面临同样的选择时，似乎多以延缓重构而告终——当然这也是一种选择。我的观点则与营地法则无异：保证离开时的代码库一定比你来时更加健康。完美的境界很难达到，但应该时时都勤加拂拭。