Question

我正在尝试将以'N'开头的列表元素整理成新列表。为什么这不起作用？

const countries = ['Norway', 'Sweden',  'Denmark', 'New Zealand'];

function firstN(){
  for (let i=0;i<countries.length;i++){
    countries[i].startsWith("N")
    }
}

let startsWithN = countries.filter(firstN())

Answer 1

这与@ adeneo的答案大致相同，只是一点点：

const countries = ['Norway', 'Sweden',  'Denmark', 'New Zealand'];

const startsWithN = countries.filter((country) => country.startsWith("N"));

console.log(startsWithN);

// Output: [ 'Norway', 'New Zealand' ]

Answer 2

您根据条件进行过滤，指定的函数会根据该条件返回true或false

＆＃13;

const countries = ['Norway', 'Sweden', 'Denmark', 'New Zealand'];

function firstN(item) {
  return item.toLowerCase().indexOf('n') === 0;
}

let startsWithN = countries.filter(firstN);

console.log(startsWithN)

＆＃13;

Answer 3

非常简单：

＆＃13;

const countries = ['Norway', 'Sweden',  'Denmark', 'New Zealand'];

let startsWithN = countries.filter(function (country) {
  return country[0].toLowerCase() === 'n';
});

console.log(startsWithN)

＆＃13;

Answer 4

countries.filter(s => s.toLowerCase().indexOf("n") == 0)

Answer 5

如果预期结果是一个新数组，其中只包含以countries开头的"N"元素，则可以调整现有javascript以在firstN内创建数组，并传递输入数组到firstN，.push()元素，在if循环中将for条件循环到新数组return新数组

＆＃13;

const countries = ['Norway', 'Sweden', 'Denmark', 'New Zealand'];

function firstN(arr, letter) {
  for (let i = 0, res = []; i < arr.length; i++) {
    if (arr[i].startsWith(letter)) res.push(arr[i])
  }
  return res
}

let startsWithN = firstN(countries, "N");

console.log(startsWithN);

＆＃13;

要对原始数组进行排序，您可以使用.sort()。

＆＃13;

const countries = ['Norway', 'Sweden', 'Denmark', 'New Zealand'];

function sortByFirstLetter(letter) {
  return function(a, b) {
    let [firstLetterA, firstLetterB] = [a[0], b[0]];
    return firstLetterA === letter && firstLetterB !== letter ? -1 : 1
  }
}

countries.sort(sortByFirstLetter("N"));

console.log(countries);

＆＃13;

Answer 6

仍然很苛刻：

const countries = ['Norway', 'Sweden',  'Denmark', 'New Zealand'];

const startsWithN = countries.filter(/./.test.bind(/^N/));

console.log(startsWithN);

这将函数传递给filter RexExp.prototype.test的curry版本：它将上下文（this）设置为/^N/，即匹配的正则表达式以大写字母N开头的字符串。结果类似于：

const startsWithN = countries.filter(country => /^N/.test(country));

Answer 7

const countries = ['Norway', 'Sweden',  'Denmark', 'New Zealand'];

const startsWithN = countries.filter((country) => country[0]==='N');

console.log(startsWithN);

Answer 8

const freinds = ['Salman', 'Asad',  'Shahrukh', 'Aman'];
const startsS = freinds.filter((freind) => freind.startsWith("s"));
console.log(startsS);

输出：

<块引用>

['萨尔曼'，'沙鲁克']

过滤以JavaScript中的字母开头的列表元素

8 个答案: