メソッドチェーンの使い方

let array = [
    { id: 1, name: 'Item 1', isActive: true, value: 10 },
    { id: 2, name: 'Item 2', isActive: false, value: 20 },
    { id: 3, name: 'Item 3', isActive: true, value: 30 },
    { id: 4, name: 'Item 4', isActive: false, value: 40 },
    { id: 5, name: 'Item 5', isActive: true, value: 50 }
];

// メソッドチェーンの実行例
let result = array
    .filter(item => item.isActive)   // isActiveがtrueのアイテムをフィルタリング
    .map(item => item.value)         // 各アイテムのvalueだけを取り出す
    .reduce((sum, value) => sum + value, 0); // valueを1つずつ加算して合計を計算する。0は初期値

console.log(result); // 90

console.log(array.filter(item => item.isActive)) /**
[
    { id: 1, name: 'Item 1', isActive: true, value: 10 },
    { id: 3, name: 'Item 3', isActive: true, value: 30 },
    { id: 5, name: 'Item 5', isActive: true, value: 50 }
]*/

console.log(array.map(item => item.value)) // [ 10, 20, 30, 40, 50 ]

let data = [
    { firstName: 'John', lastName: 'Doe', age: 25, isActive: true, pay: 100, gender: 'male' },
    { firstName: 'Jane', lastName: 'Smith', age: 30, isActive: false, pay: 200, gender: 'female' },
    { firstName: 'Tom', lastName: 'Johnson', age: 35, isActive: true, pay: 150, gender: 'male' },
    { firstName: 'Lucy', lastName: 'Brown', age: 19, isActive: true, pay: 250, gender: 'female' },
    { firstName: 'Emily', lastName: 'Davis', age: 40, isActive: true, pay: 300, gender: 'female' },
    { firstName: 'Daniel', lastName: 'Miller', age: 50, isActive: true, pay: 400, gender: 'male' },
    { firstName: 'Laura', lastName: 'Wilson', age: 22, isActive: true, pay: 500, gender: 'female' },
    { firstName: 'David', lastName: 'Moore', age: 18, isActive: true, pay: 50, gender: 'male' },
    { firstName: 'Mark', lastName: 'Taylor', age: 28, isActive: true, pay: 600, gender: 'male' },
    { firstName: 'Sophia', lastName: 'White', age: 33, isActive: true, pay: 700, gender: 'female' }
];
  

const tax = 0.10

let result = data
    .filter(item => item.gender == 'male' && item.age > 18)  // 男性で18歳以上
    .map(item => ({
        name: item.firstName + " " + item.lastName,// フルネーム作成
        pay: item.pay + (item.pay * 0.10)// taxを計算
    }))
    .sort((a, b) => b.pay - a.pay)// payの降順にソート
    .slice(0, 5)// 上位5つを取得
    .reduce((acc, current) => {
        let initials = current.name.split(" ").map(n => n[0]).join("");
        acc[initials] = current.pay;
        return acc;
    }, {});// 名前の頭文字をキーにしてpayをオブジェクトにまとめる

console.log(result); //{ MT: 660, DM: 440, TJ: 165, JD: 110 }