This feature is well established and works across many devices and browser versions. It’s been available across browsers since April 2021.
The read-only startOffset property of the AbstractRange interface returns the offset into the start node of the range's start position.
An integer value indicating the number of characters into the Node indicated by startContainer at which the first character of the range is located.
let startOffset = range.startOffset;
| Specification |
|---|
| DOM> # ref-for-dom-range-startoffset①> |
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Opera | Safari | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | WebView Android | WebView on iOS | |
startOffset |
90 | 9018–79 | 69 | 76 | 14.1 | 90 | 79 | 64 | 14.5 | 15.0 | 90 | 14.5 |
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https://developer.mozilla.org/en-US/docs/Web/API/AbstractRange/startOffset