How to implement a drop-down list to select a value in js (3 methods)_javascript skills

The example in this article describes the method of selecting a certain value in a drop-down list using js. Share it with everyone for your reference, the details are as follows:

Method 1:

<select id="aa">
<option>1</option>
<option>2</option>
</select>
<input type="button" value=" 选中" onclick="checkOption()" />
<script language="javascript" type="text/javascript" >
function checkOption()
{
 document.getElementById("aa").options[1].selected = true;
 alert("选中了2");
}
</script>

Method 2:

There is a drop down as follows

<select name="" >
<option value="1">11</option>
<option value="2">22</option>
<option value="3">33</option>
.......

Operation of mycombo drop-down list box not within the form

document.all( "mycombo ").selectedIndex=2 // 成功选中“苹果”这一项
mycombo.selectedIndex=2 // 成功选中“苹果”这一项 
document.mycombo.selectedIndex=2 // 失败 

Operation of drop-down list box combo2 within the form myform

document.all( "combo2 ").selectedIndex=2 // 成功选中“买水果”这一项
myform.combo2.selectedIndex=2 // 成功选中“买水果”这一项 
document.myform.combo2.selectedIndex=2 // 成功选中“买水果”这一项

Method 3:

Can be assigned by value.

For example:

The drop-down list code is as follows:

<select onPropertyChange="showValue(this.value)" id="mysel">
 <option value=""></option>
 <option value="1">1</option>
 <option value="2">2</option>
 <option value="3">3</option>
</select>
<input type="button" value="changevalue" onclick="setvalue();">

The JS function code is as follows:

function setvalue() {
 document.getElementById("mysel").value="2";
}

I hope this article will be helpful to everyone in JavaScript programming.