您的 ID 应该是唯一的。此外，您的 HTML 代码中不存在 ID“nameOutput”。
这里有一个快速的解决方案：
<!DOCTYPE html>
<html>
<head>
<title>Variable Output Example</title>
</head>
<body>
<h1>Variable Output Example</h1>
<label for="NameInput">Enter your name:</label>
<input id="NameInput" type="text">
<button onclick="fillData()">Submit</button>
<p>I understand your name is <span><output id="nameOutput1"></output></span>.</p>
<p>It's nice to meet you, <span><output id="nameOutput2"></output></span>.</p>
<script>
function fillData() {
var name = document.querySelector("#NameInput").value;
document.querySelector("#nameOutput1").innerHTML = name;
document.querySelector("#nameOutput2").innerHTML = name;
}
</script>
</body>
</html>const input = document.querySelector('#name-output');
input.addEventListener('input', () =>
document.querySelectorAll('.name-output').forEach(span => span.textContent = input.value)
);<input id="name-output"/>
<p>I understand your name is <span class="name-output"></span>.</p>
<p>It's nice to meet you `your text`<span class="name-output"></span>.</p>