document.getElementById is returning null

Question

Here's the relevant HTML:

<div id="navcontainer">
    <ul id="navlist">
        <li><a href="#tab1">Item one</a></li>
        <li><a href="#tab2">Item two</a></li>
        <li><a href="#tab3">Item three</a></li>
        <li><a href="#tab4">Item four</a></li>
        <li><a href="#tab5">Item five</a></li>
    </ul>
</div>

The content of vertical.js

function tabber() {
    var li = document.getElementById("navcontainer");
    var as = document.getElementById('navlist');

    return;
}

window.onload = tabber();

When the tabber() function is executed, the function call to document.getElementById returns null. Why? The element navcontainer definitely exists. Any clues?

Answer 1

Heh, the devil is in the detail. You are making a mistake while assigning the onload event.

window.onload = tabber();

will assign the result of tabber() to the onload property. Tabber() is executed straight away and not onload.

Change it to

window.onload = function() { tabber(); }

that will work.

Answer 2

You're calling the tabber function incorrectly on window load.

Change it to

window.onload = tabber;