Question

我遇到了错误：

未捕获的TypeError：无法读取第5行上未定义的属性'length'

当我将其输入控制台时。我不确定为什么将senArr[i]拆分为数组然后传递给for循环时说undefined是function LongestWord(sen) { var senArr = sen.split(' '); var longestWord = senArr[0]; for (let i = 1; i <= senArr.length; i++) { if (senArr[i].length > longestWord.length) { longestWord = senArr[i]; } } return longestWord; }。

我一直在试图找出为什么出现此错误...

-for循环有权访问父作用域

-senArr分为一个数组，我认为使用每个索引中存储的字符串的长度没有任何问题。

出于想法，我开始认为问题出在代码中的其他地方。

public function requestPassAction(Request $request, TokenGeneratorInterface $tokenGenerator = null)
{

    $email = $request->request->get('_username');
    $form = $this->createFormBuilder()
       ->add('username', EmailType::class, [
           'constraints' => [new Email(), new NotBlank()]
       ])
       ->getForm();
   $form->handleRequest($request);

   if ($form->isSubmitted() && $form->isValid()) {

       $em = $this->getDoctrine()->getManager();
       $user = $em->getRepository(User::class)
               ->findOneBy(array('username' => $email));

       if (!$user) {
           return $this->redirectToRoute("renouvellement_pass");
       }

       $user->setToken($tokenGenerator->generateToken());
       $user->setPasswordRequestedAt(new \Datetime());
       $em->flush();
       return $this->redirectToRoute("login");
   }

   return $this->render('Resetting/request.html.twig', [
       'form' => $form->createView()
   ]);

Answer 1

啊，将您的<=更改为<，因为数组中的最后一个索引是senArr.length - 1。

function LongestWord(sen) {
  var senArr = sen.split(' ');
  var longestWord = senArr[0];
  for (let i = 1; i < senArr.length; i++) {
    console.log('i is ', i, ' and word is ', senArr[i]);
    if (senArr[i].length > longestWord.length) {
      longestWord = senArr[i];
    }
  }
  return longestWord;
}

console.log(LongestWord('hi there this is a test'));

使用<=，您将超越最后一个索引（在上例中，i变为6），并且该索引处没有字符串，这就是您看到错误的原因。

Answer 2

问题是，当您与<=进行比较时，要包含数组length + 1，请注意数组是从零开始的索引，因此最后一项是length-1

Answer 3

你在这里...

var LongestWord = (sen) => { 
    var senArr = sen.split(' ');

    console.log(senArr);

    var longestWord = '';
    for (let i = 0; i <= senArr.length - 1; i++) {
       if (senArr[i].length > longestWord.length) {
           longestWord = senArr[i];   
       } 
    } return longestWord; 
}


console.log(LongestWord('alongword is the longest'));

Answer 4

我刚刚将其转换为现代javascript，它的工作原理是：-）

public class AssemblyTextFileReader
{
    private readonly Assembly _assembly;

    public AssemblyTextFileReader(Assembly assembly)
    {
        _assembly = assembly ?? throw new ArgumentNullException(nameof(assembly));
    }

    public async Task<string> ReadFileAsync(string fileName)
    {
        var resourceName = _assembly.GetManifestResourceName(fileName);

        using (var stream = _assembly.GetManifestResourceStream(resourceName))
        {
            using (var reader = new StreamReader(stream))
            {
                return await reader.ReadToEndAsync();
            }
        }
    }
}

public static class AssemblyExtensions
{
    public static string GetManifestResourceName(this Assembly assembly, string fileName)
    {
        string name = assembly.GetManifestResourceNames().SingleOrDefault(n => n.EndsWith(fileName, StringComparison.InvariantCultureIgnoreCase));

        if (string.IsNullOrEmpty(name))
        {
            throw new FileNotFoundException($"Embedded file '{fileName}' could not be found in assembly '{assembly.FullName}'.", fileName);
        }

        return name;
    }
}

将参数拆分为数组，现在在子范围内获得未定义

4 个答案: