重构第一个示例

[
  {
    "customer": "BigCo",
    "performances": [
      {
        "playId": "hamlet",
        "audience": 55
      },
      {
        "playId": "as-like",
        "audience": 35
      },
      {
        "playId": "othello",
        "audience": 40
      }
    ]
  }
]

{
  "hamlet": {"name":  "Hamlet", "type": "tragedy"},
  "as-like": {"name":  "As You Like It", "type": "comedy"},
  "othello": {"name":  "Othello", "type": "tragedy"}
}

const invoices = require('./invoices.json')
const plays = require('./plays.json')

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(`unknow 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;
}

console.log(statement(invoices[0], plays));