Array Cardio Day 1

JavaScript 中的Array運用
DEMO

方法	功能	備註
filter	過濾
map	重組
sort	排序
reduce	累加值計算	需要initial value

reduce

// Array.prototype.reduce()
// 4. How many years did all the inventors live all together?
const totalYears = inventors.reduce((total, inventor) => {
    return total + (inventor.passed - inventor.year);
}, 0);

計算交通工具使用次數

// 8. Reduce Exercise
// Sum up the instances of each of these
const data = ['car', 'car', 'truck', 'truck', 'bike', 'walk', 'car', 'van', 'bike', 'walk', 'car', 'van', 'car', 'truck'];
const transportation = data.reduce((obj, item) => {
    if (!obj[item]) {
        obj[item] = 0
    }
    obj[item]++;
    return obj
}, {});

知識點