zufällige Zeichenkette

function zufall() {

var str = random(); 
return str;

}

    <script type="text/javascript">
       function setRandom(){
           return Math.round(Math.random()*(122-48))+48;
       }
          
       function zufall(z){
          var chars = new Array();
          var x=0;
          var y=0;
          
          while(chars.length!=z){
              var num =  setRandom();
              if((num>47 && num<58) || (num>65 && num<91) || (num>96 && num<123)){
                  if((num>47 && num<58)&&(x<2)){
                      chars.push(String.fromCharCode(num));
                      x++;
                  }else if(y<z-2){
                      chars.push(String.fromCharCode(num));
                      y++;
                  }
              }
          }
          return chars.join('');
       }
       
//Demoaufrufe
       alert(zufall(6));
       alert(zufall(7));
       alert(zufall(8));
    </script>