[Basic JavaScript control operations]-Select operations

Select operations:

1. verify the existence ---> isexistvalue (selectobj, value );
2. register a new item ---> addnewitem (selectobj, selecttext, selectvalue );
3. Remove items ---> deleteitem (selectobj, selectvalue );
4. Delete the selected item ---> deleteselecteditem (selectobj );
5. Set item to the first item ---> setselectedfirst (selectobj, value );
6. Set item as the selected item ---> setselecteditem (selectobj, value );
7. Clear Select ---> clearselect (selectobj );

Detailed description:

Selectobj is the select control object var selectobj = Document. getelementbyid ('select1 ');

1. verify the existence
Function isexistvalue (selectobj, value)
{
VaR isexist = false;
For (VAR I = 0; I <selectobj. Options. length; I ++)
{
If (selectobj. Options [I]. value = value)
{
Isexist = true;
}
}
Return isexist;
}

2. register a new project
Function addnewitem (selectobj, selecttext, selectvalue)
{
If (isexistvalue (selectobj, selectvalue ))
{
Alert ("existing value:" + selectvalue );
Return false;
}
VaR opt = New Option (selecttext, selectvalue)
Selectobj. Options. Add (OPT)
}

3. Remove items
Function deleteitem (selectobj, selectvalue)
{
If (! Isexistvalue (selectobj, selectvalue ))
{
Alert ("This item does not exist! ");
Return false;
}
For (VAR I = 0; I <selectobj. Options. length; I ++)
{
If (selectobj. Options [I]. value = selectvalue)
Selectobj. Options. Remove (I );
}
}

4. Delete selected items
Function deleteselecteditem (selectobj)
{
If (selectobj. Options. Length = 0)
{
Alert ("no data! ");
Return false;
}
VaR Index = selectobj. Options. selectedindex;
Var val = selectobj. Options [Index]. value;
If (isexistvalue (selectobj, Val ))
{
Alert ("deleted successfully:" + val );
Selectobj. Options. Remove (INDEX );
}
Else
{
Alert ("not found! ");
}
}
5. Set item to the first item.
Function setselectedfirst (selectobj, value)
{
If (! Isexistvalue (selectobj, value )){
Alert ("This item does not exist! ");
Return false;
}
VaR Len = selectobj. Options. length;
For (VAR I = 0; I <Len; I ++)
{
If (selectobj. Options [I]. value = value)
{
Selectobj. Options [I]. Selected = true;
Break;
}
}
}

6. Set item as the selected item
Function setselecteditem (selectobj, value)
{
If (! Isexistvalue (selectobj, value )){
Alert ("This item does not exist! ");
Return false;
}
VaR Len = selectobj. Options. length;
For (VAR I = 0; I <Len; I ++)
{
If (selectobj. Options [I]. value = value)
{
Selectobj. textvalue = value;
Break;
}
}
}

7. Clear select
Function clearselect (selectobj)
{
Selectobj. Options. Length = 0;
}