JavaScipt30(第四个案例)（主要知识点：数组原型链上的一些方法）

承接上文，下面是第四个案例

附上项目链接: https://github.com/wesbos/JavaScript30

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: 'Hammarstr枚m', 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
　　// 这里有点问题,15世纪应该是1400到1500
    const fifteen = inventors.filter(inventor => (inventor.year >= 1500 && inventor.year < 1600));
    console.table(fifteen);
// Array.prototype.map()
    // 2. Give us an array of the inventor first and last names
    const fullNames = inventors.map(inventor => `${inventor.first} ${inventor.last}`);
    console.log(fullNames);

    // Array.prototype.sort()
    const ordered = inventors.sort((a, b) => a.year > b.year ? 1 : -1);
    console.table(ordered);

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

    // 5. Sort the inventors by years lived
    const oldest = inventors.sort(function(a, b) {
      const lastInventor = a.passed - a.year;
      const nextInventor = b.passed - b.year;
      return lastInventor > nextInventor ? -1 : 1;
    });
    console.table(oldest);

    // 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(link => link.textContent)
    //             .filter(streetName => streetName.includes('de'));

    // 7. sort Exercise
    // Sort the people alphabetically by last name
    const alpha = people.sort((lastOne, nextOne) => {
      const [aLast, aFirst] = lastOne.split(', ');
      const [bLast, bFirst] = nextOne.split(', ');
      return aLast > bLast ? 1 : -1;
    });
    console.log(alpha);

    // 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', 'pogostick'];

    const transportation = data.reduce(function(obj, item) {
      if (!obj[item]) {
        obj[item] = 0;
      }
      obj[item]++;
      return obj;
    }, {});

    console.log(transportation);

备注： 

1.本个案例出现好几次sort方法,我仔细看了下,不管是判断a > b,还是a - b,返回1就是正序,返回-1就是倒序
因为a > b,返回1,b会排到a之前（如果 compareFunction(a, b) 大于 0 ， b 会被排列到 a 之前）,说明小的排到前面,正序
2.这些方法都可以链式操作,不用重新定义变量承载,应及时改变观念,例子6
3.箭头函数其实已经暗含了return 操作,不用重新return,使代码更简洁
4.reduce是个不错的方法,遇到计数的例子要及时想到,如例子8,合理利用数组的各个操作方法,使代码更有逼格

转载于:https://www.cnblogs.com/wangxi01/p/10642964.html