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Home >Web Front-end >HTML Tutorial >Detailed explanation of how to set the default selected options for the tag in HTML

黄舟
黄舟Original
2017-07-28 09:18:473457browse

There are two methods.

The first method is to set the selected item through the attribute of 221f08282418e2996498697df914ce4e. This method can control the output results as needed in the background in dynamic languages ​​such as php. 

< select  id =  "sel" >
< option  value = "1" >1</ option >
< option  value = "2"  selected = "selected" >2</ option >
< option  value = "3" >3</ option >
</ select >


The second method is to control the selected item through front-end js:

< 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()"  />

The js code to obtain the text of the selected item in the 221f08282418e2996498697df914ce4e label is:

var  val = document.all.Item.options[document.all.Item.selectedIndex].text
var  i=document.getElementById( &#39;sel&#39; ).options[document.getElementById( &#39;sel&#39; ).selectedIndex].value;

Some other techniques for operating the 221f08282418e2996498697df914ce4e tag are as follows:

1) Dynamically create select

function  createSelect(){
var  mySelect = document.createElement( "select" );
mySelect.id =  "mySelect" ;
document.body.appendChild(mySelect);
}

2) Add option option

function  addOption(){
//根据id查找对象，
var  obj=document.getElementById( &#39;mySelect&#39; );
//添加一个选项
obj.add( new  Option( "文本" , "值" ));
}

3) Delete all options option

function  removeAll(){
var  obj=document.getElementById( &#39;mySelect&#39; );
obj.options.length=0;
}

4) Delete one option option

function  removeOne(){
var  obj=document.getElementById( &#39;mySelect&#39; );
//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) Get the value of option option

var  obj=document.getElementById( &#39;mySelect&#39; );
var  index=obj.selectedIndex;  //序号，取当前选中选项的序号
var  val = obj.options[index].value;

6) Get the text of option option

var  obj=document.getElementById( &#39;mySelect&#39; );
var  index=obj.selectedIndex;  //序号，取当前选中选项的序号
var  val = obj.options[index].text;

7) Modify option option

var  obj=document.getElementById( &#39;mySelect&#39; );
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) Delete select

function  removeSelect(){
var  mySelect = document.getElementById( "mySelect" );
mySelect.parentNode.removeChild(mySelect);
}

The above is the detailed content of Detailed explanation of how to set the default selected options for the