Question

我必须返回来自欧洲的JavaScript开发人员的数量。我有一个包含4个对象的数组。（名称，国家和语言等）

//以供参考并澄清问题

var list1 = [
  { firstName: 'Noah', lastName: 'M.', country: 'Switzerland', 
continent: 'Europe', age: 19, language: 'JavaScript' },
  { firstName: 'Maia', lastName: 'S.', country: 'Tahiti', continent: 
'Oceania', age: 28, language: 'JavaScript' },
  { firstName: 'Shufen', lastName: 'L.', country: 'Taiwan', 
continent: 'Asia', age: 35, language: 'HTML' },
  { firstName: 'Sumayah', lastName: 'M.', country: 'Tajikistan', 
continent: 'Asia', age: 30, language: 'CSS' }
];

//我的下面的代码

function countDevelopers(list) {

   let euro = 0;

   for( let coder = 0; coder < list.length; coder++ ){
     list[coder]["continent"];
       if( list[coder]["continent"] == 'Europe' ){
         for (let lang = 0; lang < list[coder].length; lang++ ){
           list[lang]["language"];
             if( list[coder][lang]["language"] == 'Javascript'){
               euro++;
             }
         }
       }
   }

   return euro;

}

Answer 1

您可以通过reduce调用来实现此功能：

let count = list1.reduce(
    (sum, person) => {
        let european_using_javascript = person.continent === 'Europe' && person.language === 'JavaScript';

        // `Number(boolean)` returns `1` if true, and `0` if false
        // Can also use `+european_using_javascript` unary operator, or
        // `european_using_javascript ? 1 : 0`
        return sum + Number(european_using_javascript);
    },

    // Initialize the accumulator to `0`
    0
);

console.log(count);

Answer 2

让我们看一下您的代码当前正在做什么：

function countDevelopers(list) {

  let euro = 0;
     for( let coder = 0; coder < list.length; coder++ ){

它遍历了所有编码器的整个列表。

list[coder]["continent"];

此行绝对不执行任何操作；您可以将其删除。

if( list[coder]["continent"] == 'Europe' ){
    for (let lang = 0; lang < list[coder].length; lang++ ){

如果当前的编码器来自欧洲，那么您将再次遍历所有编码器-等待。您觉得这对吗？您只需要知道此编码器是否使用JavaScript，就不必费心看所有其他编码器。它们与该编码器无关。

list[lang]["language"];

另一行什么也不做，可以删除。

if( list[coder][lang]["language"] == 'Javascript'){

什么是list[coder][lang]？编码器和lang都是从头到尾遍历整个数组索引的变量。假设您使用的是第二个编码器（索引1）和第一个lang编码器（索引0），那么这是在请求list[1][0].language。但是列表中的每个元素都是一个对象，而不是一个数组，因此没有索引0。这行没有意义。

编码的最后一部分是递增euro，就可以了。

因此，您真正需要的只是一个循环：

for (let coder = 0; coder < list.length; coder++) {
  if (list[coder].continent === 'Europe' && list[coder].language === 'JavaScript') {
    euro++;
  }
}

（如果您想花哨的话，可以通过Array.reduce操作使其更加简洁：

let euro = list.reduce((total, coder) => total + (coder.continent === 'Europe' && coder.language === 'JavaScript') ? 1 : 0, 0);

）

Answer 3

迭代项目，如果用户所在的洲是欧洲，并且语言是Javascript，则将计数增加1：

function countDevelopers(list) {
  let count = 0;

  for(var i = 0; i < list1.length; i++){
    const user = list1[i];
    if(user.continent === 'Europe' && user.language === 'JavaScript') {
      count += 1;
    }
  }

  return count; 
}

const list1 = [{"firstName":"Noah","lastName":"M.","country":"Switzerland","continent":"Europe","age":19,"language":"JavaScript"},{"firstName":"Maia","lastName":"S.","country":"Tahiti","continent":"Oceania","age":28,"language":"JavaScript"},{"firstName":"Shufen","lastName":"L.","country":"Taiwan","continent":"Asia","age":35,"language":"HTML"},{"firstName":"Sumayah","lastName":"M.","country":"Tajikistan","continent":"Asia","age":30,"language":"CSS"}];

const result = countDevelopers(list1);

console.log(result);

Answer 4

有两种方法，一种用foreach，另一种用reduce。

   var list1 = [{
    firstName: 'Noah',
    lastName: 'M.',
    country: 'Switzerland',
    continent: 'Europe',
    age: 19,
    language: 'JavaScript'
},
{
    firstName: 'Maia',
    lastName: 'S.',
    country: 'Tahiti',
    continent: 'Oceania',
    age: 28,
    language: 'JavaScript'
},
{
    firstName: 'Shufen',
    lastName: 'L.',
    country: 'Taiwan',
    continent: 'Asia',
    age: 35,
    language: 'HTML'
},
{
    firstName: 'Sumayah',
    lastName: 'M.',
    country: 'Tajikistan',
    continent: 'Asia',
    age: 30,
    language: 'CSS'
}
];

const countDev = (x) => {
  let count = 0;
  x.forEach(x => {
      if (x.continent === "Europe" && x.language === "JavaScript") count++
  })
  return count;
}

console.log(countDev(list1))

// OR

const countDev1 = (x) => {

  return x.reduce((accum, x) => {
    if (x.continent === "Europe" && x.language === "JavaScript") return ++accum;
    return accum;
  }, 0)

}

console.log(countDev1(list1))

Answer 5

您可以使用过滤器，并具有提供国家和语言的通用功能

    var list1 = [
      { firstName: 'Noah', lastName: 'M.', country: 'Switzerland', 
    continent: 'Europe', age: 19, language: 'JavaScript' },
      { firstName: 'Maia', lastName: 'S.', country: 'Tahiti', continent: 
    'Oceania', age: 28, language: 'JavaScript' },
      { firstName: 'Shufen', lastName: 'L.', country: 'Taiwan', 
    continent: 'Asia', age: 35, language: 'HTML' },
      { firstName: 'Sumayah', lastName: 'M.', country: 'Tajikistan', 
    continent: 'Asia', age: 30, language: 'CSS' }
    ];

    function countDevelopers(list, continent, language) {
return list.filter(developer => {return developer.continent == continent && developer.language == language}).length
    }


console.log(countDevelopers(list1, 'Europe', 'JavaScript'));

访问数组内部的对象数据

5 个答案: