JavaScript如何获取选区的偏移量？

Question

场景出现在一个富文本编辑器种，我要选中一段文本，选中之后在选中的文本中间上方出现一个tooltips

不清楚应该使用哪种方法获取一个selection（选区）的起始点和结束点相较于body的偏移量（不是字符偏移量）,从而定位tooltips元素。

Answer 1

const getSelection = root => {
  let t = null;
  if (root.getSelection) {
    t = root.getSelection();
  } else if (root.document.getSelection) {
    t = root.document.getSelection();
  } else if (root.document.selection) {
    t = root.document.selection.createRange().text;
  }
  return t;
};

const getSelectionRect = selection => {
  if (selection.rangeCount <= 0) {
    return null;
  }

  const _rect = selection.getRangeAt(0).getBoundingClientRect();
  let rect = _rect && _rect.top ? _rect : selection.getRangeAt(0).getClientRects()[0];
  if (!rect) {
    if (selection.anchorNode && selection.anchorNode.getBoundingClientRect) {
      rect = selection.anchorNode.getBoundingClientRect();
    } else {
      return null;
    }
  }
  return rect;
};

// 获取选择
const selection = getSelection(window);
// 获取选择区域边界
const selectionRect = getSelectionRect(selection);

Answer 2

$(selector).offset()