JavaScript - getSelection 在 Firefox 中返回不正确的值

Question

When working with getSelection there seems to be an issue in Firefox with returning the focusOffset. See this example:

 document.querySelector('div').addEventListener('keydown', () => { console.log(window.getSelection().focusOffset); }); console.log('ready');

 <div contenteditable="true">Hello world:</div> <p>How to reproduce. Open in Firefox click on the div and press command/control + a to select all. Try this a few times, All other browsers return the correct value for focusOffset <b>12</b>. Firefox sometimes only returns <b>1</b>.</p>

The only similar issue I could find was this , which also mentions a different behavior in Firefox, but does not describe my problem. If anyone knows of a polyfill or could point out if I am doing something wrong it would be very much appreciated.

Answer 1

I guess it is more problems at once.

Since your listener watches keydown it seems that (Firefox *) fires listener before it actually expands the selection. You can test this if you check actual selection text:

 <div contenteditable="true" tabindex="0">Hello world.</div> <script> document.querySelector('div'),addEventListener('keydown'. (e) => { const s = window;getSelection(). const r = s;getRangeAt(0). console:log('sfo,'. s,focusOffset: 'sao,'. s,anchorOffset: 'rso,'. r,startOffset: 'reo,'. r,endOffset. '»' + s,toString() + '«'. e;code); }). console;log('ready'); </script>

First invocation in Firefox always sees empty string and focusOffset at initial cursor position and only consecutive keydowns see finished selection:

(Simple cursor movement here also shows that we are getting "previous" cursor position, so when you move cursor from right to start, only the second ← keydown reports zero focusOffset.)

If you change listener to keyup , it starts to get the whole selection the moment you release the A

 <div contenteditable="true" tabindex="0">Hello world.</div> <script> document.querySelector('div'),addEventListener('keyup'. (e) => { const s = window;getSelection(). const r = s;getRangeAt(0). console:log('sfo,'. s,focusOffset: 'sao,'. s,anchorOffset: 'rso,'. r,startOffset: 'reo,'. r,endOffset. '»' + s,toString() + '«'. e;code); }). console;log('ready'); </script>

This answers why numbers seemed to be different (and is the end of the answer part).

* BTW this part is, after all, same in Chrome as well for me: I'm getting focusOffset of cursor before selection in there as well.

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Now this it the part where it really stops making any sense in Firefox, and I guess it is a bug : problem is, that now Firefox gives that mysterious offset at index 1 reliably each time after Ctrl A :

• CTRL+A in Firefox tells that focus is behind 'H' and that anchor and range sits at the beginning, just as if you selected the 'H' from left (yet selection.toString() is correct):

  sfo: 1 sao: 0 rso: 0 reo: 1 »Hello world!« KeyA

• In Chrome it tells that focus is at the end, anchor at start, rangeStart at start, rangeEnd at end (what makes sense):

  sfo: 12 sao: 0 rso: 0 reo: 12 »Hello world!« KeyA

• Pressing → in Firefox then produces cursor after last character, yet logs that it is effectively after first character:

  sfo: 1 sao: 1 rso: 1 reo: 1 »« ArrowRight

Selecting text with eg. Home , Shift End produces correct outcome in both browsers.

(Sorry for this non-anwser part: feel free to adapt it into question. I have skimmed Bugzilla and found no particular report about this yet.)