Question

I am using the innerHTML function to dynamically create a drop-down menu in HTML and populate it with certain parameters. Here is my code:

for (i in categories) {
    var cat_name = i;
    var cats = categories[cat_name];

    P2_txt.innerHTML += cat_name;       

    if (cats.length > 2) {
        // Drop Down Menu Needed
        P2_txt.innerHTML += '<select>';

        for (var j = 0; j < cats.length; j++) {
            P2_txt.innerHTML += '<option>'+cats[j]+'</option>';
        }

        P2_txt.innerHTML += '</select>';
    }   
}

However when I run it, the following HTML code is generated:

<select></select>
<option>Value of cats[0]</option>
<option>Value of cats[1]</option>
<option>Value of cats[2]</option>

Instead of what I want, which is this:

<select>
    <option>Value of cats[0]</option>
    <option>Value of cats[1]</option>
    <option>Value of cats[2]</option>
</select>

Any thoughts?

Answer 1

When you modify innerHTML it’s immediately parsed into the DOM… so you’ve effectively added a select element followed by a bunch of option elements out of the intended hierarchy.

So, you either:

1. Build your entire combobox markup and then add it to
   innerHTML
2. or use the DOM methods createElement and
   appendChild and so forth instead of ugly string concatenation.

var categories = {
    "Domestic": ["Tabby", "Siamese"],
    "Wild": ["Cougar", "Tiger", "Cheetah"]
  },
  cats,
  combo,
  frag = document.createDocumentFragment();

for (var category in categories) {

  cats = categories[category];

  frag.appendChild(document.createTextNode(category));

  combo = document.createElement("select");

  for (var i = 0, ln = cats.length; i < ln; i++) {
    combo.appendChild(document.createElement("option")).textContent = cats[i];
  }

  frag.appendChild(combo);
}

document.body.appendChild(frag);

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