我有一个带有选择的创建元素的表单。 我该怎么做才能创建一次元素？

Question

I have JS code which creates paragraph and input elements according to html. But I need this code to create each element only once.

Peace of Javascript code

function comFunction(sel) {
   switch (sel.value) {
        case 'skype':
            var skype = document.createElement("P");
            var temp = document.createTextNode("Enter your skype");
            var input = document.createElement("input");
            input.type = "text";
            skype.appendChild(temp);
            form.appendChild(skype);
            form.appendChild(input);
            break;
}

HTML code

<form id="form">
<select name="liason" id="liason" onchange="comFunction(this);">
    <option value="skype">Skype</option>
    <option value="icq">ICQ</option>
    <option value="facebook">Facebook</option>
    <option value="email">e-mail</option>
</select>
</form>

Answer 1

If you add an id to the elements being created and appended to the DOM, you can then check for their existence before running the code that would create them a second time:

 function comFunction(sel) {

   switch (sel.value) {
    case 'skype':
        if(document.getElementById("skypeParagraph") === null) {
           var skype = document.createElement("P");
           skype.setAttribute("id", "skypeParagraph");
           var temp = document.createTextNode("Enter your skype");
           var input = document.createElement("input");
           input.type = "text";
           skype.appendChild(temp);
           form.appendChild(skype);
           form.appendChild(input);
        }
        break;
 }