Sergey1986,
<style>
table{
border-collapse: collapse;
}
td{
border: 1px solid gray;
}
</style>
<table id="tab">
<tr><td>34,5</td><td>3,5</td><td>36</td><td>23</td></tr>
<tr><td>34,5</td><td>3,5</td><td>36</td><td>23</td></tr>
<tr><td>34,5</td><td>3,5</td><td>36</td><td>23</td></tr>
</table>
<script>
var tds = [...tab.querySelectorAll('td')];
function idx(td) {
return tds.indexOf(td)
}
tab.onmouseup = e => {
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tr = start.parentNode,
stop = getSelection().focusNode;
stop = stop.tagName == 'TD'? stop:stop.parentNode;
start = idx(start);
stop = idx(stop);
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arr = [...tr.querySelectorAll('td')]
.filter(e => idx(e) >= min && idx(e) <= max)
.map(e => e.textContent);
console.log(arr);
};
</script>