javascript get child by id

<div onclick="test(this)">
    <div id="child">child</div>

I want to change the style of the child div when the parent div is clicked. How do I reference it? I would like to be able to reference it by ID as the the html in the parent div could change and the child won't be the first child etc.

function test(el){
  el.childNode["child"].style.display = "none";

Something like that, where I can reference the child node by id and set the style of it.


EDIT: Point taken with IDs needing to be unique. So let me revise my question a little. I would hate to have to create unique IDs for every element that gets added to the page. The parent div is added dynamically. (sort of like a page notes system). And then there is this child div. I would like to be able to do something like this: el.getElementsByName("options").item(0).style.display = "block";

If I replace el with document, it works fine, but it doesn't to every "options" child div on the page. Whereas, I want to be able to click the parent div, and have the child div do something (like go away for example).

If I have to dynamically create a million (exaggerated) div IDs, I will, but I would rather not. Any ideas?


In modern browsers (IE8, Firefox, Chrome, Opera, Safari) you can use querySelector():

function test(el){
  el.querySelector("#child").style.display = "none";

For older browsers (<=IE7), you would have to use some sort of library, such as Sizzle or a framework, such as jQuery, to work with selectors.

As mentioned, IDs are supposed to be unique within a document, so it's easiest to just use document.getElementById("child").