在本书第1版中，我使用的示例程序是为影片出租店的顾客打印一张详单。放到今天，很多人可能要问了：“影片出租店是什么？”为了避免过多回答这个问题，我翻新了一下示例，将其包装成一个仍有古典韵味又尚未消亡的现代示例。 设想有一个戏剧演出团，演员们经常要去各种场合表演戏剧。通常客户（customer）会指定几出剧目，而剧团则根据观众（audience）人数及剧目类型来向客户收费。该团目前出演两种戏剧：悲剧（tragedy）和喜剧（comedy）。给客户发出账单时，剧团还会根据到场观众的数量给出“观众量积分”（volume credit）优惠，下次客户再请剧团表演时可以使用积分获得折扣——你可以把它看作一种提升客户忠诚度的方式。 该剧团将剧目的数据存储在一个简单的JSON文件中。 ##### plays.json... ```json { "hamlet": {"name": "Hamlet", "type": "tragedy"}, "as-like": {"name": "As You Like It", "type": "comedy"}, "othello": {"name": "Othello", "type": "tragedy"} } ``` 他们开出的账单也存储在一个JSON文件里。 ##### invoices.json... ```json [ { "customer": "BigCo", "performances": [ { "playID": "hamlet", "audience": 55 }, { "playID": "as-like", "audience": 35 }, { "playID": "othello", "audience": 40 } ] } ] ``` 下面这个简单的函数用于打印账单详情。 ```js function statement (invoice, plays) { let totalAmount = 0; let volumeCredits = 0; let result = `Statement for ${invoice.customer}\n`; const format = new Intl.NumberFormat( "en-US", { style: "currency", currency: "USD", minimumFractionDigits: 2 }).format; for (let perf of invoice.performances) { const play = plays[perf.playID]; let thisAmount = 0; switch (play.type) { case "tragedy": thisAmount = 40000; if (perf.audience > 30) { thisAmount += 1000 * (perf.audience - 30); } break; case "comedy": thisAmount = 30000; if (perf.audience > 20) { thisAmount += 10000 + 500 * (perf.audience - 20); } thisAmount += 300 * perf.audience; break; default: throw new Error(`unknown type: ${play.type}`); } // add volume credits volumeCredits += Math.max(perf.audience - 30, 0); // add extra credit for every ten comedy attendees if ("comedy" === play.type) volumeCredits += Math.floor(perf.audience / 5); // print line for this order result += ` ${play.name}: ${format(thisAmount/100)} (${perf.audience} seats)\n`; totalAmount += thisAmount; } result += `Amount owed is ${format(totalAmount/100)}\n`; result += `You earned ${volumeCredits} credits\n`; return result; } ``` 用上面的数据文件（`invoices.json`和`plays.json`）作为测试输入，运行这段代码，会得到如下输出： ``` Statement for BigCo Hamlet: $650.00 (55 seats) As You Like It: $580.00 (35 seats) Othello: $500.00 (40 seats) Amount owed is $1,730.00 You earned 47 credits ```