SOURCE

function moveNumbers()
{
var no=document.getElementById("no")
var option=no.options[no.selectedIndex].text
var txt=document.getElementById("result").value
txt=txt + option
document.getElementById("result").value=txt
}

<form>
   请选择数字：
  <br> 
  <select id="no"> <option>0</option> <option>1</option> <option>2</option> <option>3</option> <option>4</option> <option>5</option> <option>6</option> <option>7</option> <option>8</option> <option>9</option> </select> 
  <input type="button" onclick="moveNumbers()" value="-->"> 
  <input type="text" id="result" size="20"> 
 </form>