如何修复“无法读取null的属性'addEventListener'”错误
Gou*_*kur 0 html javascript ecmascript-6
我正在从Mozilla开发人员网络（MDN）学习javascript。我在数字猜谜游戏中遇到错误。该错误在第46行显示“未捕获的TypeError：无法读取null的属性'addEventListener'”。
我已经逐行检查并匹配了很多代码，但是我无法解决问题。当我删除script.js外部文件并将代码放入标签内的index.html中时，代码部分起作用（某些功能不起作用）。这是代码。请理解，JavaScript代码和HTML位于不同的文件中。
let randomNumber = Math.floor(Math.random() * 100) + 1;
const guesses = document.querySelector('.guesses');
const lastResult = document.querySelector('.lastResult');
const loworHi = document.querySelector('.loworHi');
const guessSubmit = document.querySelector('.guessSubmit');
const guessField = document.querySelector('.guessField');
let guessCount = 1;
let resetButton;
function checkGuess() {
let userGuess = Number(guessField.value);
if (guessCount === 1) {
guesses.textContent = 'Previous guesses: ';
}
guesses.textContent += userGuess + ' ';
if (userGuess === randomNumber) {
lastResult.textContent = 'Congratulations! You got it right!';
lastResult.style.backgroundColor = 'green';
loworHi.textContent = '';
setGameOver();
} else if (guessCount === 10) {
lastResult.textContent = '!!!GAME OVER!!!';
setGameOver();
} else {
lastResult.textContent = 'Wrong!';
lastResult.style.backgroundColor = 'red';
if (userGuess < randomNumber) {
loworHi.textContent = 'Last guess was too low!';
} else if (userGuess > randomNumber) {
loworHi.textContent = 'Last guess was too high!';
}
}
guessCount++;
guessField.value = '';
guessField.focus();
}
guessSubmit.addEventListener('click', checkGuess);
function setGameOver() {
guessField.disabled = true;
guessSubmit.disabled = true;
resetButton = document.createElement('button');
resetButton.textContent = 'Start new game';
document.body.appendChild(resetButton);
resetButton.addEventListener('click', resetGame);
}
function resetGame() {
guessCount = 1;
const resetParas = document.querySelectorAll('.resultParas p');
for (let i = 0; i < resetParas.length; i++) {
resetParas[i].textContent = '';
}
resetButton.parentNode.removeChild(resetButton);
guessField.disabled = false;
guessSubmit.disabled = false;
guessField.value = '';
guessField.focus();
lastResult.style.backgroundColor = 'white';
randomNumber = Math.floor(Math.random() * 100) + 1;
}
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<link rel="stylesheet" type="text/css" href="style.css">
<script type="text/javascript" src="script.js"></script>
<title>Number guessing game</title>
</head>
<body>
<h1>Number guessing game</h1>
<p>We have selected a random number between 1 and 100. See if you can guess it in 10 turns or fewer.
We'll tell you if your guess was too high or too low.</p>
<div class="form">
<label for="guessField">Enter a guess: </label>
<input type="text" id="guessField" class="guessField">
<input type="submit" value="Submit guess" class="guessSubmit">
</div>
<div class="resultParas">
<p class="guesses"></p>
<p class="lastResult"></p>
<p class="lowOrHi"></p>
</div>
</body>
</html>
小智 5
您正在加载<head>HTML正文之前，将Javascript文件加载到中。因此你的线
const guessSubmit = document.querySelector('.guessSubmit');
没有什么可查找的-您带有类的按钮guessSubmit尚不存在。并且由于guessSubmit为null，因此不包含任何属性，因此会出现错误。
最简单的解决方案是将<script>标签放在HTML主体的底部而不是头部的底部。这样，它将在DOM完全加载后加载Javascript。
其他方法包括添加事件侦听器以在DOM加载后运行脚本，例如DOMContentLoaded。在此处查看更多信息：https : //developer.mozilla.org/en-US/docs/Web/Events/DOMContentLoaded。