javascript - How can I decrypt this JS? -

How can I decode this JS? I know what it does (check it with alert) and decrypt it and edit it. How can I do this?

What kind of encryption is this? I know that there are many decrypters that see but none of them managed to decrypt this one.

BTW I am a newbie.

  function xViewState () {var a = 0, m, v, t, z, x = new array ('+ 9 91968376', '8887918192818786347374918784939277359287883421333333338896', '877,886,888787', '949990793917947998942577939317') , L = x.length; While (++ A and LT; = L) {M = x [L - A]; T = z = ''; For (v = 0; v & lt; m.length;) {t + = m.charAt (v ++); If (t.length == 2) {z + = String.fromCharCode (parseInt (t) + 25 - L + a); T = ''; }} X [l - a] = z; } Document.write ('& lt;' + [[0] + '' + [4] + '' + '' + '[x + 2] +' {'+ x [1] +'} & lt; / '+ X [0] +' & gt; '); } XViewState (); Text after "   
 
 
 This is not encryption, this is the story. Now you know what it is written, losing ambiguity and just writing that what you want instead ...  
  document.write ('& gt; style undefined & gt; Yourstylename {position: absolute; top: -9999px} & lt; / style & gt; ');   
 Obscencing works by listing ASCII codes for everything, approximately 20 (each array element varies), 2 points as decimal number. It is very basic.  
 Like this:  
  "style" - & gt; 115, 116, 121, 108, 101 (ASCII code) - & gt; 90, 91, 96, 83, 76 (in this case, offset of 25 years)