How to Get the Start and End Offsets of a Selection within its Parent Container?

Get a Range's Start and End Offsets Relative to Its Parent Container

In HTML documents, user selections can extend across different elements and text nodes. Determining the exact range in characters within the parent container of the selection can be challenging. However, we can utilize various techniques to achieve this regardless of browser variations.

One approach involves cloning the selection range and setting its end points to the start and end of the parent container. By comparing the resulting text contents with the original selection range, we can calculate the start and end offsets relative to the parent. Here's an example in JavaScript:

function getSelectionCharacterOffsetWithin(element) {
  var start = 0;
  var end = 0;
  var preCaretRange = range.cloneRange();
  preCaretRange.selectNodeContents(element);
  preCaretRange.setEnd(range.startContainer, range.startOffset);
  start = preCaretRange.toString().length;
  preCaretRange.setEnd(range.endContainer, range.endOffset);
  end = preCaretRange.toString().length;
  return { start: start, end: end };
}

This method provides both the start and end offsets within the parent container, accounting for HTML tags and text node traversal. It can be employed in a variety of applications that require precise character offsets, such as text editing tools and content manipulation scripts.

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