javascript implements the indentation of tab key in textarea

The example of javascript illustrates the indentation method of tab key in textarea. Share to everybody for everybody reference. The details are as follows:

Search the Internet for 1 related solution, others use 2 or 3 lines of javascript solution, but all have 1 minor problem. And JQuery, which is also very concise.

The javascript code in this article implements the ability to enter the TAB key in TEXTAREA and indent it automatically. However, this code does not execute properly in the Google browser

sel =event.srcElement.document.selection.createRange()

This one will make an error:
ncaught exception TypeError: Cannot read property 'selection' of undefined

The code executes normally in IE as follows:

<mce:script type="text/javascript">
<!-- 
function editTab() 
{ 
  var code, sel, tmp, r 
  var tabs="" 
  event.returnValue = false 
  sel =event.srcElement.document.selection.createRange() 
  r = event.srcElement.createTextRange() 
  switch (event.keyCode) 
  { 
    case (8)  : 
      if (!(sel.getClientRects().length > 1)) 
      { 
        event.returnValue = true 
        return 
      } 
      code = sel.text 
      tmp = sel.duplicate() 
      tmp.moveToPoint(r.getBoundingClientRect().left, sel.getClientRects()[0].top) 
      sel.setEndPoint("startToStart", tmp) 
      sel.text = sel.text.replace(/^/t/gm, "") 
      code = code.replace(/^/t/gm, "").replace(//r/n/g, "/r") 
      r.findText(code) 
      r.select() 
      break 
    case (9)  : 
      if (sel.getClientRects().length > 1) 
      { 
        code = sel.text 
        tmp = sel.duplicate() 
        tmp.moveToPoint(r.getBoundingClientRect().left, sel.getClientRects()[0].top) 
        sel.setEndPoint("startToStart", tmp) 
        sel.text = "/t"+sel.text.replace(//r/n/g, "/r/t") 
        code = code.replace(//r/n/g, "/r/t") 
        r.findText(code) 
        r.select() 
      } 
      else 
      { 
        sel.text = "/t" 
        sel.select() 
      } 
      break 
    case (13)  : 
      tmp = sel.duplicate() 
      tmp.moveToPoint(r.getBoundingClientRect().left, sel.getClientRects()[0].top) 
      tmp.setEndPoint("endToEnd", sel) 
      for (var i=0; tmp.text.match(/^[/t]+/g) && i<tmp.text.match(/^[/t]+/g)[0].length; i++)  tabs += "/t" 
      sel.text = "/r/n"+tabs 
      sel.select() 
      break 
    default   : 
      event.returnValue = true 
      break 
  } 
} 
// -->
</mce:script>

When using:

<textarea cols=80 rows=20 name="input" onkeydown="editTab()"></textarea>

I hope this article has been helpful for your javascript programming.