怎么让两个独立选中的select option互换（可以实时）

我想用一个按键互换select选中的内容

像这样

有数据的时候也可以实时变化

最好用js

我的代码

<TABLE>
<TBODY> 
<TR class="inputa"> 
	<TH><b></b></TH>
<TD> 
<INPUT name=input onchange="convert(this.form,form.measure1, form.measure2)" size=30>
</TD>
<TD> 
<SELECT name=measure1 
 onchange="convert(this.form,this, form.measure2)">
<OPTION selected value=0.0001>cm ^2

<OPTION value=1>m ^2

<OPTION value=10000>km ^2

<OPTION value=0.0929>feets ^2

<OPTION value=0.8361>yds ^2 

<OPTION value=2589988.11>mi ^2

</OPTION>
</SELECT>
</TD>
</TR>
<TR class="inputb"> 
	<TH ><b></b></TH>
<TD> 
<INPUT name=display size=30>
</TD>
<TD> 
<SELECT name=measure2 
 onchange="convert(this.form,form.measure1, this)">
 <OPTION value=0.0001>cm ^2

    <OPTION value=1>m ^2
    
    <OPTION value=10000>km ^2
    
    <OPTION selected value=0.0929>feets ^2
    
    <OPTION value=0.8361>yds ^2 
    
    <OPTION value=2589988.11>mi ^2

    </OPTION>
</SELECT>
</TD>
</TR>
</TBODY> 
</TABLE>

懂了。代码编写中。

基本搞定。

https://paste.ubuntu.com/p/PkPcp3QYSX/

<TABLE>
<TBODY> 
<TR class="inputa"> 
	<TH><b></b></TH>
<TD> 
<INPUT name=input onchange="convert(this.form,form.measure1, form.measure2)" size=30>
</TD>
<TD> 
<SELECT name=measure1 
 onchange="convert(this.form,this, form.measure2)">
<OPTION selected value=0.0001>cm ^2
 
<OPTION value=1>m ^2
 
<OPTION value=10000>km ^2
 
<OPTION value=0.0929>feets ^2
 
<OPTION value=0.8361>yds ^2 
 
<OPTION value=2589988.11>mi ^2
 
</OPTION>
</SELECT>
</TD>
</TR>
<TR class="inputb"> 
	<TH ><b></b></TH>
<TD> 
<INPUT name=display size=30>
</TD>
<TD> 
<SELECT name=measure2 
 onchange="convert(this.form,form.measure1, this)">
 <OPTION value=0.0001>cm ^2
 
    <OPTION value=1>m ^2
    
    <OPTION value=10000>km ^2
    
    <OPTION selected value=0.0929>feets ^2
    
    <OPTION value=0.8361>yds ^2 
    
    <OPTION value=2589988.11>mi ^2
 
    </OPTION>
</SELECT>
</TD>
</TR>
<TR>
<TD>
<input type="button" value="交换" onclick="swap(this.form);" />
<script type="text/javascript">
function swap(form) {
	var t = form.measure1.value;
	form.measure1.value = form.measure2.value;
	form.measure2.value = t;
	convert(form,form.measure1, form.measure2)
}
</script>
<TD>
</TR>
</TBODY> 
</TABLE>

test