"Go" JS in the basic operation of Select

Determine if the item value= "Paravalue" exists in the Select option

//1. Determine if the value= "Paravalue" item exists in the SELECT optionfunctionJsselectisexititem (Objselect, objitemvalue) {varIsexit =false;  for(vari = 0; i < objSelect.options.length; i++) {                if(Objselect.options[i].value = =objitemvalue) {Isexit=true;  Break; }            }            returnIsexit; }      

Add an item to the Select option

//2. Add an item to the Select optionfunctionJsadditemtoselect (Objselect, Objitemtext, objitemvalue) {//determine if there is    if(Jsselectisexititem (Objselect, Objitemvalue)) {alert ("The value of the item already exists"); } Else {                varVaritem =NewOption (Objitemtext, Objitemvalue);             ObjSelect.options.add (Varitem); Alert ("Join successfully"); }        }       

Remove an item from the Select option

//3. Remove an item from the Select optionfunctionJsremoveitemfromselect (Objselect, objitemvalue) {//determine if there is    if(Jsselectisexititem (Objselect, Objitemvalue)) { for(vari = 0; i < objSelect.options.length; i++) {                    if(Objselect.options[i].value = =objitemvalue)                        {ObjSelect.options.remove (i);  Break; }} alert ("Successfully deleted"); } Else{alert ("The item does not exist in this select"); }        }    

Delete selected items in select

// 4. Delete the selected    item in select function Jsremoveselecteditemfromselect (objselect) {            var length = Objselect.options.length-1;         for (var i = length; I >= 0; i--) {            iftrue) {                 NULL ;            }        }    }      

Modify the Select option in Value = " Paravalue " the text is " Paratext "  

//5. Modify the text of value= "Paravalue" in the Select option to "Paratext"functionJsupdateitemtoselect (Objselect, Objitemtext, objitemvalue) {//determine if there is    if(Jsselectisexititem (Objselect, Objitemvalue)) { for(vari = 0; i < objSelect.options.length; i++) {                    if(Objselect.options[i].value = =objitemvalue) {Objselect.options[i].text=Objitemtext;  Break; }} alert ("Successful Modification"); } Else{alert ("The item does not exist in this select"); }        }        

set text in select = " Paratext " The first item is selected

//6. Set the first item of text= "Paratext" in Select to be selectedfunctionJsselectitembyvalue (Objselect, objitemtext) {//determine if there is    varIsexit =false;  for(vari = 0; i < objSelect.options.length; i++) {                if(Objselect.options[i].text = =Objitemtext) {objselect.options[i].selected=true; Isexit=true;  Break; }            }                  //Show out Results    if(isexit) {alert ("Selected successfully"); } Else{alert ("The item does not exist in this select"); }        }        

set value in select = " Paravalue " the item is selected

// 7. Set the item of value= "Paravalue" in Select to    select Document.all.objSelect.value = Objitemvalue;    

gets the value of the currently selected item of select

// 8. Gets the value    of the current selected item of select var currselectvalue = Document.all.objSelect.value;    

Gets the text of the current selected item of select

// 9. Gets the text    of the current selected item of select var currselecttext = Document.all.objselect.options[document.all.objselect.selectedindex].text;    

Gets the index of the current selected item of select

// 10. Get the index    of the current selected item of select var currselectindex = Document.all.objSelect.selectedIndex;    

Empty the Select item

// 11. Clear the Select item     document.all.objSelect.options.length = 0;