在检验本文框为0或正整数时,不知为什么alert的提示信息会出现二次?在线等

<form name="form1" method="post" action="../controller/sjmanage?action=add">
  <table width="90%" height="706" border="0" align="center" cellpadding="0" cellspacing="0">
    <tr>
      <td width="8%" height="40">试卷名称:</td>
      <td width="44%"><input name="sjname" type="text" id="sjname"></td>
      <td width="48%">&nbsp;</td>
    </tr>
    <tr>
      <td height="39">&nbsp;</td>
      <td>&nbsp;</td>
      <td>&nbsp;</td>
    </tr>
    <tr>
      <td height="39">总分:</td>
      <td><input name="full" type="text" id="full"  readonly /></td>
      <td>总题量:
        <input name="questionnumber" type="text" id="questionnumber"  readonly/></td>
    </tr>
    <tr>
      <td colspan="3">一、单选题：（总分：
      <input name="tx1score" type="text" id="tx1score" readonly >
       　
      数量： 
       <input name="tx1number" type="text" id="tx1number" readonly >
      ）
      <input name="tx1txname" type="hidden" id="tx1txname" value="单选题"></td>
    </tr>
    <tr>
      <td height="36" colspan="3"><table width="90%" height="154" border="0" cellpadding="0" cellspacing="0">
        <tr>
          <td>1分题：</td>
          <td><input name="tx1number1" type="text" id="tx1number1" onblur="addDigit1()"/></td>
        </tr>
        <tr>
          <td width="10%">2分题:</td>
          <td width="90%"><input name="tx1number2" type="text" id="tx1number2" onblur="addDigit1()"></td>
          </tr>
        <tr>
          <td>3分题:</td>
          <td><input name="tx1number3" type="text" id="tx1number3" onblur="addDigit1()"></td>
          </tr>
        <tr>
          <td>4分题:</td>
          <td><input name="tx1number4" type="text" id="tx1number4" onblur="addDigit1()"></td>
          </tr>
        <tr>
          <td>5分题:</td>
          <td><input name="tx1number5" type="text" id="tx1number5" onblur="addDigit1()"></td>
          </tr>
        <tr>
          <td colspan="2">&nbsp;</td>
          </tr>
      </table></td>
    </tr>
    <tr>
      <td height="29" colspan="3">二、多选题：（总分：
        <input name="tx2score" type="text" id="tx2score" readonly >
　
      数量：
<input name="tx2number" type="text" id="tx2number" readonly >
）
<input name="tx2txname" type="hidden" id="tx2txname" value="多选题"></td>
    </tr>
    <tr>
      <td colspan="3"><table width="90%" height="154" border="0" cellpadding="0" cellspacing="0">
        <tr>
          <td>1分题：</td>
          <td><input name="tx2number1" type="text" id="tx2number1" onblur="addDigit2()"></td>
        </tr>
        <tr>
          <td width="10%">2分题:</td>
          <td width="90%"><input name="tx2number2" type="text" id="tx2number2" onblur="addDigit2()"></td>
        </tr>
        <tr>
          <td>3分题:</td>
          <td><input name="tx2number3" type="text" id="tx2number3" onblur="addDigit2()"></td>
        </tr>
        <tr>
          <td>4分题:</td>
          <td><input name="tx2number4" type="text" id="tx2number4" onblur="addDigit2()"></td>
        </tr>
        <tr>
          <td>5分题:</td>
          <td><input name="tx2number5" type="text" id="tx2number5" onblur="addDigit2()"></td>
        </tr>
        <tr>
          <td colspan="2">&nbsp;</td>
        </tr>
      </table></td>
    </tr>
    <tr>
      <td height="23" colspan="3">三、判断题：（总分：
        <input name="tx3score" type="text" id="tx3score" readonly >
　
      数量：
<input name="tx3number" type="text" id="tx3number" readonly >
）
<input name="tx3txname" type="hidden" id="tx3txname" value="判断题"></td>
    </tr>
    <tr>
      <td height="25" colspan="3"><table width="90%" height="154" border="0" cellpadding="0" cellspacing="0">
        <tr>
          <td>1分题：</td>
          <td><input name="tx3number1" type="text" id="tx3number1" onblur="addDigit3()"></td>
        </tr>
        <tr>
          <td width="10%">2分题:</td>
          <td width="90%"><input name="tx3number2" type="text" id="tx3number2" onblur="addDigit3()"></td>
        </tr>
        <tr>
          <td>3分题:</td>
          <td><input name="tx3number3" type="text" id="tx3number3" onblur="addDigit3()"></td>
        </tr>
        <tr>
          <td>4分题:</td>
          <td><input name="tx3number4" type="text" id="tx3number4" onblur="addDigit3()"></td>
        </tr>
        <tr>
          <td>5分题:</td>
          <td><input name="tx3number5" type="text" id="tx3number5" onblur="addDigit3()"></td>
        </tr>
        <tr>
          <td colspan="2">&nbsp;</td>
        </tr>
      </table></td>
    </tr>
    <tr>
      <td height="22" colspan="3"><input type="submit" name="Submit" value="提交">
      <input type="reset" name="Submit2" value="重置"></td>
    </tr>
    <tr>
      <td height="23">&nbsp;</td>
      <td>&nbsp;</td>
      <td>&nbsp;</td>
    </tr>
    <tr>
      <td height="22">&nbsp;</td>
      <td>&nbsp;</td>
      <td>&nbsp;</td>
    </tr>
    <tr>
      <td height="27">&nbsp;</td>
      <td>&nbsp;</td>
      <td>&nbsp;</td>
    </tr>
  </table>
</form>
</body>
</html>