JavaScript operation select dropdown box Operation application

JS Code
//

1. Determine if there is a value= "Paravalue" Item in the Select option
function Jsselectisexititem (Objselect, Objitemvalue) {
var isexit = false;
for (var i = 0; i < objSelect.options.length; i++) {
if (Objselect.options[i].value = = Objitemvalue) {
Isexit = true;
Break
}
}
return isexit;
}

2. Add an item to the Select option
function Jsadditemtoselect (Objselect, Objitemtext, Objitemvalue) {
To determine whether there is
if (Jsselectisexititem (Objselect, Objitemvalue)) {
Alert ("The value of the item already exists");
} else {
var varitem = new Option (Objitemtext, Objitemvalue);
ObjSelect.options.add (Varitem);
Alert ("Join successfully");
}
}

3. Remove an item from the Select option
function Jsremoveitemfromselect (Objselect, Objitemvalue) {
To determine whether there is
if (Jsselectisexititem (Objselect, Objitemvalue)) {
for (var i = 0; i < objSelect.options.length; i++) {
if (Objselect.options[i].value = = Objitemvalue) {
ObjSelect.options.remove (i);
Break
}
}
Alert ("Successful deletion");
} else {
Alert ("The item does not exist in the select");
}
}

4. Delete selected items in select
function Jsremoveselecteditemfromselect (objselect) {
var length = objselect.options.length-1;
for (var i = length; I >= 0; i--) {
if (objselect[i].selected = = True) {
Objselect.options[i] = null;
}
}
}

5. Modify the Select option Value= "Paravalue" text is "Paratext"
function Jsupdateitemtoselect (Objselect, Objitemtext, Objitemvalue) {
To determine whether there is
if (Jsselectisexititem (Objselect, Objitemvalue)) {
for (var i = 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 the select");
}
}

6. Set the first item of text= "Paratext" in Select to select
function Jsselectitembyvalue (Objselect, Objitemtext) {
To determine whether there is
var isexit = false;
for (var i = 0; i < objSelect.options.length; i++) {
if (Objselect.options[i].text = = Objitemtext) {
Objselect.options[i].selected = true;
Isexit = true;
Break
}
}
Show the results
if (isexit) {
Alert ("Successfully selected");
} else {
Alert ("The item does not exist in the select");
}
}

7. Set the item of value= "Paravalue" in Select to select
function Check () {
var c = document.all.objSelect;
for (var i=0;i<c.options.length; i++) {
if (C.options (i). Value==paravalue) {
C.selectedindex =i;
}
}
}

8. Value of the current selected item of the Select
var currselectvalue = Document.all.objSelect.value;

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

10. Index of the current selected item for select
var currselectindex = Document.all.objSelect.selectedIndex;

11. Empty a Select item
document.all.objSelect.options.length = 0;