<script type="text/javascript">
function a(object){
alert(object);
}
</script>

<!-- 獲取顯示的值 -->
<select onchange="a(this.options[this.selectedIndex].innerText);">
<option value="value-a">text-a</option>
<option value="value-b">text-b</option>
</select>

<!-- 獲取value的值 -->
<select onchange="a(this.options[this.selectedIndex].value);">
<option value="value-c">text-c</option>
<option value="value-d">text-d</option>
</select>

function isSelect(selectPress) {
            //var select = document.getElementById("mySelect").ind;
            var selectValue = selectPress.options[selectPress.selectedIndex].value; //顯示value 下標0、1、2
            var selectValue2 = selectPress.options[selectPress.selectedIndex].innerText; //顯示顯示的值 具體內容(上海、北京)
            //alert(selectValue);
            //alert(selectValue2);
            if (selectValue == "-1") {
                alert("請選擇城市，表單提交被拒絕！")
                return;
            }
            else {
                document.getElementById('form1').submit(); //form表單提交
            }
        }

<select onchange="isSelect(this);" id="mySelect">
        <option value="-1">--請選擇--</option>
        <option value="0">北京</option>
        <option value="1">上海</option>
        <option value="2">武漢</option>
</select>