javascript数组includes、reduce的基本使用

// ES5 Code
const numbers = ["一", "二", "三", "四"];
console.log(numbers.indexOf("一") > -1); // true
console.log(numbers.indexOf("六") > -1); // false

// ES7 Code
console.log(numbers.includes("一")); // true
console.log(numbers.includes("六")); // false

console.log(numbers.includes("一",1)); // false，从数组索引为`1`往后找
console.log(numbers.includes("一", -3)); // true，从 `array.length + fromIndex` 的索引开始完后找，跟上面从索引为1开始等效

// 过去
const day = "星期二";
if (day === "星期二" || day === "星期三" || day === "星期四") {
    console.log(day);
}

// 现在
if (["星期二", "星期三", "星期四"].includes(day)) {
    console.log(day);
}

const arrNumbers = [1, 2, 3, 4, 5];
const reduceNumbers = (arrayNumbers, accumulatorInitVal = false) => {
    const reduceCallback = (accumulator, currentVal, currentIndex) => {
        console.log(`当前索引：${currentIndex}`);
        return accumulator + currentVal;
    };
    return accumulatorInitVal
        ? arrayNumbers.reduce(reduceCallback, accumulatorInitVal)
        : arrayNumbers.reduce(reduceCallback);
};

console.log(reduceNumbers(arrNumbers)); // 15，累计器初始值为数组的第一个元素的值1
console.log(reduceNumbers(arrNumbers, 10)); // 25，累计器初始值为10

const users = [
    {
        firstName: "坚",
        lastName: "孙",
        age: 37,
    },
    {
        firstName: "策",
        lastName: "孙",
        age: 21,
    },
    {
        firstName: "葛亮",
        lastName: "诸",
        age: 28,
    },
    {
        firstName: "备",
        lastName: "刘",
        age: 44,
    },
    {
        firstName: "统",
        lastName: "庞",
        age: 22,
    },
    {
        firstName: "维",
        lastName: "姜",
        age: 19,
    },
    {
        firstName: "伯温",
        lastName: "刘",
        age: 22,
    },
];
const getFullName = (user) => `${user.lastName}${user.firstName}`;
const filterByAge = (user) => user.age >= 20 && user.age < 30;

// 常规实现
const getFilterResult = users
    //  第一步筛选年龄20-30之间的用户
    .filter((user) => filterByAge(user))
    //  拼接全名
    .map((user) => getFullName(user))
    //  筛选
    .filter((fullName) => fullName.length === 3);

console.log(getFilterResult);   // [ '诸葛亮', '刘伯温' ]

// 迭代方式实现
const iterationsFilterResult = (arrayResult, currentUser) => {
    const fullname = getFullName(currentUser);
    if (filterByAge(currentUser) && fullname.length === 3) {
        arrayResult.push(fullname);
    }
    return arrayResult;
};
console.log(users.reduce(iterationsFilterResult, []));  // [ '诸葛亮', '刘伯温' ]