// 判断select选项中 是否存在Value="paraValue"的Item
function jsSelectIsExitItem(objSelect, objItemValue) {       
    var isExit = false;       
    for (var i = 0; i < objSelect.options.length; i++) {       
        if (objSelect.options[i].value == objItemValue) {       
            isExit = true;       
            break;       
        }       
    }       
    return isExit;       
}        
// 向select选项中 加入一个Item
function jsAddItemToSelect(objSelect, objItemText, objItemValue) {       
    //判断是否存在       
    if (jsSelectIsExitItem(objSelect, objItemValue)) {       
        alert("该Item的Value值已经存在");       
    } else {       
        var varItem = new Option(objItemText, objItemValue);     
        objSelect.options.add(varItem);    
        alert("成功加入");    
    }       
}       
// 从select选项中 删除一个Item       
function jsRemoveItemFromSelect(objSelect, objItemValue) {       
    //判断是否存在       
    if (jsSelectIsExitItem(objSelect, objItemValue)) {       
        for (var i = 0; i < objSelect.options.length; i++) {       
            if (objSelect.options[i].value == objItemValue) {       
                objSelect.options.remove(i);       
                break;       
            }       
        }       
        alert("成功删除");       
    } else {       
        alert("该select中 不存在该项");       
    }       
}   
// 删除select中选中的项   
function jsRemoveSelectedItemFromSelect(objSelect) {
var length = objSelect.options.length - 1;   
    for(var i = length; i >= 0; i--){   
        if(objSelect[i].selected == true){   
            objSelect.options[i] = null;   
        }   
    }   
}
// 修改select选项中 value="paraValue"的text为"paraText"       
function jsUpdateItemToSelect(objSelect, objItemText, objItemValue) {
    if (jsSelectIsExitItem(objSelect, objItemValue)) {       
        for (var i = 0; i < objSelect.options.length; i++) {       
            if (objSelect.options[i].value == objItemValue) {       
                objSelect.options[i].text = objItemText;       
                break;       
            }       
        }       
        alert("成功修改");       
    } else {       
        alert("该select中 不存在该项");       
    }       
}
// 设置select中text="paraText"的第一个Item为选中       
function jsSelectItemByValue(objSelect, objItemText) {                 
    var isExit = false;       
    for (var i = 0; i < objSelect.options.length; i++) {       
        if (objSelect.options[i].text == objItemText) {       
            objSelect.options[i].selected = true;       
            isExit = true;       
            break;       
        }       
    }
    if (isExit) {       
        alert("成功选中");       
    } else {       
        alert("该select中 不存在该项");       
    }       
}       
//设置select中value="paraValue"的Item为选中   
document.all.objSelect.value = objItemValue;   
//得到select的当前选中项的value   
var currSelectValue = document.all.objSelect.value;   
//得到select的当前选中项的text   
var currSelectText = document.all.objSelect.options[document.all.objSelect.selectedIndex].text;   
//得到select的当前选中项的Index
var currSelectIndex = document.all.objSelect.selectedIndex;
//清空select的项   
document.all.objSelect.options.length = 0;