fallback composition state

一、作用

二、初始化

export function initialize(nativeEventTarget) {
  root = nativeEventTarget;
  startText = getText();
  return true;
}

三、重置

export function reset() {
  root = null;
  startText = null;
  fallbackText = null;
}

四、获取数据

export function getData() {
  if (fallbackText) {
    return fallbackText;
  }

  let start;
  const startValue = startText;
  const startLength = startValue.length;
  let end;
  const endValue = getText();
  const endLength = endValue.length;

  for (start = 0; start < startLength; start++) {
    if (startValue[start] !== endValue[start]) {
      break;
    }
  }

  const minEnd = startLength - start;
  for (end = 1; end <= minEnd; end++) {
    if (startValue[startLength - end] !== endValue[endLength - end]) {
      break;
    }
  }

  const sliceTail = end > 1 ? 1 - end : undefined;
  fallbackText = endValue.slice(start, sliceTail);
  return fallbackText;
}

五、获取文本

export function getText() {
  if ('value' in root) {
    return root.value;
  }
  return root.textContent;
}

六、变量

1. 根

/**
 * These variables store information about text content of a target node,
 * allowing comparison of content before and after a given event.
 *
 * 这些变量存储目标节点的文本内容信息，允许在特定事件前后比较内容。
 *
 * Identify the node where selection currently begins, then observe
 * both its text content and its current position in the DOM. Since the
 * browser may natively replace the target node during composition, we can
 * use its position to find its replacement.
 *
 * 确定当前选择开始的节点，然后观察它的文本内容以及在 DOM 中的当前位置。由于浏览器在输入法编辑过程
 * 中可能会原生替换目标节点，我们可以使用它的位置来找到其替代节点。
 *
 *
 */

// 根
let root = null;
// 开始文本
let startText = null;
// 备选文本
let fallbackText = null;