How to set the default selected option based on the select tag?

Below I will share with you an article on how to set the default selected option for the select tag. It has a good reference value and I hope it will be helpful to everyone.

There are two methods.

##The first sets the selected item through the attribute of . This method can be used in dynamic languages ​​such as php in the background according to Need to control the output results.

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

The second type 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 get the text of the selected item in the tag is:

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

Some other techniques for operating the

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( 'mySelect' );
//添加一个选项
obj.add( new Option( "文本" , "值" ));
}

3) Delete all options option

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

4) Delete an option 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) Get the value of 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].value;

6) Get the text of 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].text;

7) Modify option 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) Delete select

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

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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