A complete collection of Javascript operation select methods [add, modify, delete, select, clear, determine existence, etc.]_Form special effects

js code
// 1. Determine whether there is an Item with Value="paraValue" in the select option
function jsSelectIsExitItem(objSelect, objItemValue) {
var isExit = false;
for (var i = 0; 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 ) {
//Determine whether it exists
if (jsSelectIsExitItem(objSelect, objItemValue)) {
alert("The Value of this Item already exists");
} else {
var varItem = new Option(objItemText, objItemValue);
objSelect.options.add(varItem);
alert("Successfully added");
}
}

/ / 3. Delete an Item from the select option
function jsRemoveItemFromSelect(objSelect, objItemValue) {
//Determine whether it exists
if (jsSelectIsExitItem(objSelect, objItemValue)) {
for ( var i = 0; i if (objSelect.options[i].value == objItemValue) {
objSelect.options.remove(i);
break ;
}
}
alert("Deleted successfully");
} else {
alert("This item does not exist in the selection");
}
}


// 4. Delete the selected item in the 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 text of value="paraValue" in the select option to "paraText"
function jsUpdateItemToSelect(objSelect, objItemText, objItemValue ) {
//Determine whether it exists
if (jsSelectIsExitItem(objSelect, objItemValue)) {
for (var i = 0; i if (objSelect .options[i].value == objItemValue) {
objSelect.options[i].text = objItemText;
break;
}
}
alert("Successfully modified");
} else {
alert("This item does not exist in the selection");
}
}

// 6. Set text="paraText" in the select "The first Item is selected
function jsSelectItemByValue(objSelect, objItemText) {
//Determine whether it exists
var isExit = false;
for (var i = 0; i if (objSelect.options[i].text == objItemText) {
objSelect.options[i].selected = true;
isExit = true;
break;
}
}
//Show the result
if (isExit) {
alert("Successfully selected");
} else {
alert(" This item does not exist in the selection");
}
}

// 7. Set the Item with value="paraValue" in the selection to be selected
document .all.objSelect.value = objItemValue;

// 8. Get the value of the currently selected item of select
var currSelectValue = document.all.objSelect.value;

// 9. Get the text of the currently selected item of select
var currSelectText = document.all.objSelect.options[document.all.objSelect.selectedIndex].text;

/// 10. Get the Index of the currently selected item of select
var currSelectIndex = document.all.objSelect.selectedIndex;

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