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Question

window.onload != <body onload="">

Answer 1

A:

I think the window object is created before any actual elements are parsed.

pavpanchekha 2009-10-27 22:01:45

i would assume so as well, however it is well aware that the collection exists, that is what confuses me.

Andrej Marinic 2009-10-27 22:03:48

Answer 2

+6 A:

window.onload = getSpanElements();

should be

window.onload = getSpanElements;

The code you have calls the getSpanElements function and assigns its return value as the onload event handler.

David Dorward 2009-10-27 22:04:31

absolutely right! thanks :)

Andrej Marinic 2009-10-27 22:09:55

Answer 3

+1 A:

You might want to move your window.onload assignment below the getSpanElements declaration:

<html>
<script type="text/javascript">


        function getSpanElements(){
                var collectionBoolean = document.getElementsByTagName("span")?true:false;
                alert(
                        "collection exists? " + collectionBoolean + "; number of collection members: " + document.getElementsByTagName("span").length
                );
        }

        window.onload = getSpanElements;

</script>
<head>
        <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
        <title>Untitled Document</title>
</head>
<body onload="getSpanElements()">
        <span> test </span>
</body>

At the point in your code where you're assigning the window.onload event handler, getSpanElements() has not yet been defined. Also, the line should be

window.onload=getSpanElements;

not

window.onload=getSpanElements();

The function name without parentheses is a reference to the function. With parentheses, it executes the function and the return value is assigned to window.onload.

David Lively 2009-10-27 22:05:34

Since getSpanElements is defined with the function statement rather than the function expression, it is subject to hoisting — so it doesn't need appear before the assignment in the code order.

David Dorward 2009-10-27 22:09:44

yes, i made a call instead of a reference. thank you!

Andrej Marinic 2009-10-27 22:10:31

Answer 4

+7 A:

You're setting the function wrong:

window.onload = getSpanElements();

should be

window.onload = getSpanElements;

You're setting the onload handler to the return value of getSpanElements() at the moment.

Greg 2009-10-27 22:05:46

absolutely right! thanks :)

Andrej Marinic 2009-10-27 22:09:12

Answer 5

+1 A:

You're wrongly doing this:

window.onload = getSpanElements();

which sets the window.onload to the result of the call to the function getSpanElements (undefined).

You should do this instead:

window.onload = getSpanElements;

Seb 2009-10-27 22:06:22

actually, the function returns `undefined`, not `null`

Christoph 2009-10-27 22:08:34

Edited now, thanks Christoph :)

Seb 2009-10-27 22:09:50

Answer 6

A:

You have to assign a reference to the function getSpanElements to window.onload - currently, the function doesn't get executed onload, but immediately after parsing.

What you actually assign is the undefined return value.

In short: drop the ().

Christoph 2009-10-27 22:06:58

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window.onload != <body onload="">

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