我不断收到错误消息：TypeError：无法在 Javascript 中读取 null 的属性“长度”

Question

I have looked at the other threads. I am a longtime lurker, this is the first time I'm posting (I think) or it's been a while. Anyways, I know what the problem is, I think, based on the other responses, it would seem that my variable isn't initialized. But I don't think this is my issue.

I am trying to create a "Guess the word" game, similar to hangman without the stick figure. I am creating a function that sees how many times the letter is in the word. I'm not sure if I'm doing it right. Please look at my code and tell me what I'm doing wrong...?

Thank you!

function timesInWord(word, letter) {
  var re = new RegExp(letter,"gi");
  var isMatch = word.match(re).length;

if (isMatch != null && isMatch > 0) {
 return isMatch;
 } else {
 return "No Match, Try again!";
 }
}

console.log(timesInWord("Mississippi","r"));

Answer 1

word.match(re) will return null if there are no matches. That's the cause of the problem. If you want to check if there are matches, before getting the length of the array, check if it's not null .

Answer 2

When there is no match found word.match(re) returns null . Trying to call length on null causes the error.

You do not need to use length property. In your case only the null checking is enough. Try the following:

 function timesInWord(word, letter) { var re = new RegExp(letter,"gi"); var isMatch = word.match(re); if (isMatch != null) { return isMatch.length; } else { return "No Match, Try again!"; } } console.log(timesInWord("Mississippi","p"));