使用 :has() 为父级设置样式

Web 功能： :user-valid 和 :user-invalid

问题

通常，错误状态需要设置输入框外部元素的样式，例如更改父级 fieldset 边框的颜色、突出显示 <label>，或在卡片标题中显示全局错误图标。过去，这需要 JavaScript 在父元素上切换类。

解决方案

通过将 :has() 与 :user-invalid 结合使用，我们可以根据特定后代的有效性状态，以声明方式设置任何祖先元素的样式。这样可以将所有呈现逻辑保留在 CSS 中。

实施策略

  1. 选择器：使用 .parent:has(:user-invalid) 定位到容器。
  2. 范围：请具体说明，以免出现性能问题。定位到 .field-group，而不是 body。
  3. 后备：如果不支持 :has()，则需要使用 JS 在父级上切换类。

实现指南

1. HTML 结构

<form>
  <div class="card-section">
    <div class="header">
      <h3>Profile Settings</h3>
      <span class="status-icon"></span>
    </div>

    <div class="field">
      <label for="username">Username</label>
      <input type="text" id="username" required>
    </div>
  </div>
</form>

2. CSS

/* Default State */
.card-section {
  border: 1px solid #ccc;
  border-left: 4px solid #ccc;
}

/*
  Parent Styling Logic:
  If the card contains ANY user-invalid input, turn the whole card's edge red.
*/
.card-section:has(:user-invalid) {
  border-left-color: #d93025;
  background-color: #fff8f8;
}

/* Change the icon too */
.card-section:has(:user-invalid) .status-icon::after {
  content: "⚠️";
}

回退和浏览器支持

后备 CSS

我们在父级上使用类 .has-error 来模拟 :has() 行为。

/* Native */
.card-section:has(:user-invalid) {
  border-left-color: #d93025;
}

/* Fallback */
.card-section.has-error-fallback {
  border-left-color: #d93025;
}

JavaScript 后备

使用可重复使用的实用程序，通过 WeakMap 跟踪互动状态。这样可以避免使用“脏”类或数据属性污染 DOM。

const UserInvalidFallback = (() => {
  const dirtyState = new WeakMap();

  const updateState = (input) => {
    const isValid = input.checkValidity();

    // Update both visual and ARIA state
    input.classList.toggle('user-invalid-fallback', !isValid);
    input.classList.toggle('user-valid-fallback', isValid);

    if (!isValid) {
      input.setAttribute('aria-invalid', 'true');
    } else {
      input.removeAttribute('aria-invalid');
    }
  };

  const handleEvent = (event) => {
    const input = event.target;

    if (event.type === 'reset') {
      const controls = input.elements || [];
      for (const control of controls) {
        dirtyState.delete(control);
        control.classList.remove('user-invalid-fallback');
        control.classList.remove('user-valid-fallback');
        control.removeAttribute('aria-invalid');
      }
      return;
    }

    if (!input.checkValidity) return;

    if (event.type === 'input' || event.type === 'change') {
      const state = dirtyState.get(input) || { hasInteracted: false, hasBlurred: false };
      state.hasInteracted = true;
      dirtyState.set(input, state);
      if (state.hasBlurred) {
        updateState(input);
      }
    } else if (event.type === 'blur') {
      const state = dirtyState.get(input) || { hasInteracted: false, hasBlurred: false };
      state.hasBlurred = true;
      dirtyState.set(input, state);
      if (state.hasInteracted) {
        updateState(input);
      }
    }
  };

  const init = (root = document) => {
    if (CSS.supports('selector(:user-invalid)')) return;

    root.addEventListener('blur', handleEvent, true); // Capture phase
    root.addEventListener('input', handleEvent);
    root.addEventListener('change', handleEvent);
    root.addEventListener('reset', handleEvent, true); // Capture resets
  };

  return { init };
})();

// Initialize for a specific form
const form = document.querySelector('#demo-form');
UserInvalidFallback.init(form);

// 1. Initialize the generic fallback
const form = document.querySelector('#demo-form');
UserInvalidFallback.init(form);

// 2. Add specialized "parent styling" logic (Separate from fallback)
// Listen for changes to form validity after interaction
form.addEventListener('blur', (e) => {
  if (!e.target.matches('input, select, textarea')) return;

  // Find the container we want to style (sync with CSS)
  const container = e.target.closest('.card-section');
  if (!container) return;

  // Check if ANY fallbacked input in this container is invalid
  const hasError = container.querySelector('.user-invalid-fallback');
  container.classList.toggle('has-error-fallback', !!hasError);
}, true); // Capture phase to ensure we run after the fallback's blur listener

// Also handle input events for immediate cleanup
form.addEventListener('input', (e) => {
  const container = e.target.closest('.card-section');
  if (container) {
    const hasError = container.querySelector('.user-invalid-fallback');
    container.classList.toggle('has-error-fallback', !!hasError);
  }
});

// Handle form resets
form.addEventListener('reset', () => {
  form.querySelectorAll('.has-error-fallback').forEach(el => {
    el.classList.remove('has-error-fallback');
  });
});

其他注意事项

  1. 无障碍功能：原生 :user-invalid 不会自动与 ARIA 属性同步。添加以下 JavaScript，使 aria-invalid 与视觉状态保持同步：
// Sync aria-invalid with the CSS :user-invalid state
const syncAria = (el) => {
  el.setAttribute?.('aria-invalid', el.matches(':user-invalid') ? 'true' : 'false');
};

// Update on blur (to show error) and input (to clear it)
document.addEventListener('blur', (e) => syncAria(e.target), true);
document.addEventListener('input', (e) => {
  if (e.target.hasAttribute('aria-invalid')) syncAria(e.target);
});