JS30 day04 - Array Cardio 1

作業內容

今天的作業就比較無趣一點，是各種有關使用陣列運算的小挑戰，在練 JS 的陣列相關語法

作業內容跟做完之後的 code 如下：

const inventors = [
  { first: 'Albert', last: 'Einstein', year: 1879, passed: 1955 },
  { first: 'Isaac', last: 'Newton', year: 1643, passed: 1727 },
  { first: 'Galileo', last: 'Galilei', year: 1564, passed: 1642 },
  { first: 'Marie', last: 'Curie', year: 1867, passed: 1934 },
  { first: 'Johannes', last: 'Kepler', year: 1571, passed: 1630 },
  { first: 'Nicolaus', last: 'Copernicus', year: 1473, passed: 1543 },
  { first: 'Max', last: 'Planck', year: 1858, passed: 1947 },
  { first: 'Katherine', last: 'Blodgett', year: 1898, passed: 1979 },
  { first: 'Ada', last: 'Lovelace', year: 1815, passed: 1852 },
  { first: 'Sarah E.', last: 'Goode', year: 1855, passed: 1905 },
  { first: 'Lise', last: 'Meitner', year: 1878, passed: 1968 },
  { first: 'Hanna', last: 'Hammarström', year: 1829, passed: 1909 }
];

const people = ['Beck, Glenn', 'Becker, Carl', 'Beckett, Samuel', 'Beddoes, Mick', 'Beecher, Henry', 'Beethoven, Ludwig', 'Begin, Menachem', 'Belloc, Hilaire', 'Bellow, Saul', 'Benchley, Robert', 'Benenson, Peter', 'Ben-Gurion, David', 'Benjamin, Walter', 'Benn, Tony', 'Bennington, Chester', 'Benson, Leana', 'Bent, Silas', 'Bentsen, Lloyd', 'Berger, Ric', 'Bergman, Ingmar', 'Berio, Luciano', 'Berle, Milton', 'Berlin, Irving', 'Berne, Eric', 'Bernhard, Sandra', 'Berra, Yogi', 'Berry, Halle', 'Berry, Wendell', 'Bethea, Erin', 'Bevan, Aneurin', 'Bevel, Ken', 'Biden, Joseph', 'Bierce, Ambrose', 'Biko, Steve', 'Billings, Josh', 'Biondo, Frank', 'Birrell, Augustine', 'Black, Elk', 'Blair, Robert', 'Blair, Tony', 'Blake, William'];

// Array.prototype.filter()
// 1. Filter the list of inventors for those who were born in the 1500's
const fifteen = inventors.filter(function(inventor){
  if (inventor.year >= 1500 && inventor.year < 1600 ){
    return true;
  };
});
console.table(fifteen);


// Array.prototype.map()
// 2. Give us an array of the inventors' first and last names
  const fullNames = inventors.map(function(inventor){
    return `${inventor.first} ${inventor.last}`
  });
  console.log(fullNames);


// Array.prototype.sort()
// 3. Sort the inventors by birthdate, oldest to youngest
  const inventorsOrder = inventors.sort(function(a, b){
    return a.year - b.year;
  });
  console.log(inventorsOrder);
// Array.prototype.reduce()
// 4. How many years did all the inventors live?
  const yearsTotal = inventors.reduce(function(accum, current){
    return (accum + (current.passed - current.year));
  }, 0);
  console.log(yearsTotal);

// 5. Sort the inventors by years lived
  const liveLonger = inventors.sort(function(a, b){
    return (a.passed - a.year) - (b.passed - b.year)
  });
  console.table(liveLonger);
// 6. create a list of Boulevards in Paris that contain 'de' anywhere in the name
// https://en.wikipedia.org/wiki/Category:Boulevards_in_Paris
  // const category = document.querySelector('.mw-category');
  // const links = Array.from(category.querySelectorAll('a'));
  // const de = links
  //             .map(function(link){return link.textContent})
  //             .filter(function(street){return street.includes("de")});
  // console.log(de);
  

// 7. sort Exercise
// Sort the people alphabetically by last name
  const peopleOrder = people.sort(function(a, b){
    const [aLast, aFirst] = a.split(", ")
    const [bLast, bFirst] = b.split(", ")
    return ( aLast > bLast) ? 1 : -1 
  });
  console.log(peopleOrder);
// 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 answer = data.reduce(function(obj, item){
  if (!obj[item]){
    obj[item] = 0;
  }
  obj[item]++;
  return obj;
},{});
console.log(answer);

學到什麼

列點如下：

JS
1. filter()這個方法等同於 ruby 的 select，要記得最後陣列裡面留下的只有那些回傳 true 的項目
2. console 除了 console.log 之外還可以 console.table 其他選項還可以參考這邊：https://developer.mozilla.org/zh-TW/docs/Web/API/Console
3. map 也要記得最後要留下來的值前面要放 return 才會成功轉換陣列！(忘記好幾次)
```
const fullNames = inventors.map(function(inventor){
  return `${inventor.first} ${inventor.last}`
});
```
1. sort() 方法裡面也是要放方法，一般來說會使用回傳 1 跟 -1 來排序
```
const inventorsOrder = inventors.sort(function(a, b){
  return a.year - b.year;
});
```
```
const peopleOrder = people.sort(function(a, b){
  const [aLast, aFirst] = a.split(", ")
  const [bLast, bFirst] = b.split(", ")
  return ( aLast > bLast) ? 1 : -1 
});
```
1. reduce() 在 js 比較不習慣的地方就是要把初始直放在最後面
```
const yearsTotal = inventors.reduce(function(accum, current){
  return (accum + (current.passed - current.year));
}, 0);
```
1. 使用 querySelectorAll 得到的 nodeList 無法使用 map 方法，必須用 Array.form 或者用打散的技巧先轉成陣列

總結

嘗試自己寫一次真的發現 JS 語法詭譎多變… 再加上各種大小不同的語法糖真的很容易讓人精神錯亂ＸＤ但目前前端除了接受 JS 之外也沒別的選擇了（嘆），繼續加油！

參考資料： https://github.com/wesbos/JavaScript30