SOURCE

const plays = { "hamlet": { "name": "Hamlet", "type": "tragedy" }, "as-like": { "name": "As You Like It", "type": "comedy" }, "othello": { "name": "Othello", "type": "tragedy" } };
const invoice = {
    "customer": "BigCo",
    "performances": [
        { "playID": "hamlet", "audience": 55 },
     { "playID": "as-like", "audience": 35 }, 
     { "playID": "othello", "audience": 40 }
     ]
};


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;
    invoice.performances.forEach( perf => {
        // const play = plays[perf.playID];
        
        let thisAmount = amountFor(perf, playFor(perf))
        // add volume credits
        volumeCredits += volumeCreditsFor(perf)
        // print line for this order
        result += ` ${playFor(perf).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;
}

function format(v) { return v};

function playFor(aPerformance) {
    return plays[aPerformance.playID]; 
}

function volumeCreditsFor(aPerformance) { 
    let result = 0; 
    result += Math.max(aPerformance.audience - 30, 0); 
    if ("comedy" === playFor(aPerformance).type) 
        result += Math.floor(aPerformance.audience / 5);
    return result; 
 }

function amountFor(aPerformance) {
    let result = 0;
    switch (playFor(aPerformance).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: ${playFor(aPerformance).type}`);
    }
    return result;
} 


console.log(statement(invoice))