Radio Buttons + Checked

I have in my page the following form:

Code:

<form action="this.php" method="get" name="newsform">
<input type="radio" name="number" value="latest" checked="true" /> 5 latest news entries<br />
<input type="radio" name="number" value="all" /> All news entries<br />
<input type="radio" name="number" value="custom" /> Custom number:
<input type="text" name="custom" size="2" maxlength="2" class="white" onchange="newsformchange()" />
<p><input type="submit" value="Submit" /></p>
</form>

and the javascript:

Code:

function newsformchange () {
if ( document.newsform.custom.length < 1 )
document.newsform.number['latest'].checked=true;
if ( document.newsform.custom.length > 0 )
document.newsform.number['custom'].checked=true;
}

but this code won't work!