js获取 当前表单的input

<form id="myForm">
  <input type="text" id="username" name="username">
</form>

<script>
  const inputElement = document.getElementById('username');
  console.log(inputElement.value);
</script>

<form>
  <input type="text" class="user-input" name="username">
</form>

<script>
  const inputElements = document.getElementsByClassName('user-input');
  for (let i = 0; i < inputElements.length; i++) {
    console.log(inputElements[i].value);
  }
</script>

<form>
  <input type="text" name="username">
</form>

<script>
  const inputElements = document.getElementsByTagName('input');
  for (let i = 0; i < inputElements.length; i++) {
    console.log(inputElements[i].value);
  }
</script>

<form>
  <input type="text" name="username">
</form>

<script>
  const inputElement = document.getElementsByName('username')[0];
  console.log(inputElement.value);
</script>

<form>
  <input type="text" class="user-input">
</form>

<script>
  const inputElement = document.querySelector('.user-input');
  console.log(inputElement.value);

  // 获取所有匹配的元素
  const inputElements = document.querySelectorAll('.user-input');
  inputElements.forEach(input => {
    console.log(input.value);
  });
</script>

window.onload = function() {
  const inputElement = document.getElementById('username');
  console.log(inputElement.value);
};

const inputElements = document.getElementsByClassName('user-input');
for (let i = 0; i < inputElements.length; i++) {
  if (inputElements[i].name === 'username') {
    console.log(inputElements[i].value);
    break;
  }
}