https://infovitamin.ru/nc.js

1function preventSelection(element){
2  var preventSelection = false;
3 function addHandler(element, event, handler){
4    if (element.attachEvent) 
5      element.attachEvent('on' + event, handler);
6    else 
7      if (element.addEventListener) 
8        element.addEventListener(event, handler, false);
9  }
10  function removeSelection(){
11    if (window.getSelection) { window.getSelection().removeAllRanges(); }
12    else if (document.selection && document.selection.clear)
13      document.selection.clear();
14  }
15  function killCtrlA(event){
16    var event = event || window.event;
17    var sender = event.target || event.srcElement;
18 if (sender.tagName.match(/INPUT|TEXTAREA/i))
19      return;
20 var key = event.keyCode || event.which;
21    if (event.ctrlKey && key == 'A'.charCodeAt(0))  // 'A'.charCodeAt(0) ìîæíî çàìåíèòü íà 65
22    {
23      removeSelection();
24 if (event.preventDefault) 
25        event.preventDefault();
26      else
27        event.returnValue = false;
28    }
29  }
30  addHandler(element, 'mousemove', function(){
31    if(preventSelection)
32      removeSelection();
33  });
34  addHandler(element, 'mousedown', function(event){
35    var event = event || window.event;
36    var sender = event.target || event.srcElement;
37    preventSelection = !sender.tagName.match(/INPUT|TEXTAREA/i);
38  });
39  addHandler(element, 'mouseup', function(){
40    if (preventSelection)
41      removeSelection();
42    preventSelection = false;
43  });
44  addHandler(element, 'keydown', killCtrlA);
45  addHandler(element, 'keyup', killCtrlA);
46}
47 
48preventSelection(document);