JS dynamically adds and deletes Option objects in select (sample code)

As shown below:

Copy the code code as follows:

//Dynamically delete all options in select:

function delAllOptions(){

document.getElementById("user_dm").options.length=0;

}

//Dynamically delete an option in the select:

function delOneOption(index){

document.getElementById("user_dm").options.remove(index);

}

//Dynamicly add item option in select:

function addOneOption(){

//document.getElementById("user_dm").options.add(new Option(2,"mytest"));

var selectObj=document.getElementById("user_dm");

alert(selectObj.length);

selectObj.options[selectObj.length] = new Option("mytest", "2");

}