html下拉框设置默认值_html下拉框怎么设置默认值

匿名用户

1级

2016-11-16 回答

第一种通过的属性来设置选中项，此方法可以在动态语言如php在后台根据需要控制输出结果。

< select id = “sel” >

< option value = “1” >1 option >

< option value = “2” selected = “selected” >2 option >

< option value = “3” >3 option >

select >

——————

第二种为通过前端js来控制选中的项:

< script type = “text/javascript” >

function change(){

document.getElementById(“sel”)[2].selected=true;

}

script >

< select id = “sel” >

< option value = “1” >1 option >

< option value = “2” >2 option >

< option value = “3” >3 option >

select >

< input type = “button” value = “修改” onclick = “change()” />

获取标签选中项文本的js代码为:

================

var val = document.all.Item.options[document.all.Item.selectedIndex].text

var i=document.getElementById( ‘sel‘ ).options[document.getElementById( ‘sel‘ ).selectedIndex].value;

一些其它操作标签的技巧如下：

1)动态创建select

================

function createSelect(){

var mySelect = document.createElement( “select” );

mySelect.id = “mySelect” ;

document.body.appendChild(mySelect);

}

2)添加选项option

================

function addOption(){

//根据id查找对象，

var obj=document.getElementById( ‘mySelect‘ );

//添加一个选项

obj.add( new Option( “文本” , “值” ));

}

3)删除所有选项option

================

function removeAll(){

var obj=document.getElementById( ‘mySelect‘ );

obj.options.length=0;

}

4)删除一个选项option

================

function removeOne(){

var obj=document.getElementById( ‘mySelect‘ );

//index,要删除选项的序号，这里取当前选中选项的序号

var index=obj.selectedIndex;

obj.options.remove(index);

}

5)获得选项option的值

================

var obj=document.getElementById( ‘mySelect‘ );

var index=obj.selectedIndex; //序号，取当前选中选项的序号

var val = obj.options[index].value;

6)获得选项option的文本

================

var obj=document.getElementById( ‘mySelect‘ );

var index=obj.selectedIndex; //序号，取当前选中选项的序号

var val = obj.options[index].text;

7)修改选项option

================

var obj=document.getElementById( ‘mySelect‘ );

var index=obj.selectedIndex; //序号，取当前选中选项的序号

var val = obj.options[index]= new Option( “新文本” , “新值” );

8)删除select

================

function removeSelect(){

var mySelect = document.getElementById( “mySelect” );

mySelect.parentNode.removeChild(mySelect);

}