Dom vs. document.getElementsByTagName

Question

Okay, since you guys are so helpful and smart, here's another
one that's got me stumped. Why does dom.getElementsByTagName work
when assigned to a variable, but document.getElementsByTagName
doesn't? Example below.
function reportSkuCondMeta() {
// Read current document's SKU_Condition meta tag
var dom = dw.getDocumentDOM(); // get the dom of the current
document
var skuCondMeta = dom.getElementsByTagName("meta");
for ( counter = 0; counter < skuCondMeta.length;
counter++)
if (skuCondMeta[counter].name == "SKU_Condition") // now I
want the DOM of the extension form
// the following code returns error "displaySku has no
properties"
var displaySku = document.getElementsByTagName("input");
for ( iter = 0; iter < displaySku.length; iter++)
if (document.displaySku[iter].name == "sku_cond")
document.displaySku[iter].value =
skuCondMeta[counter].content;
// the following code runs just fine
/* for ( iter = 0; iter <
document.getElementsByTagName("input").length; iter++)
if (document.getElementsByTagName("input")[iter].name ==
"sku_cond")
document.getElementsByTagName("input")[iter].value =
skuCondMeta[counter].content;
Of course, for ease of formatting and elegance, I want to do
the first of the two uses of document.getElementsByTagName, but I
can't get it to work. Any ideas on this would be great.
Thanks!
-Scott

Answer 1

SAX is as usefull as DOM. i first started using DOM because of the nice object model. you just have one document object and can traverse the DOM tree, look for elements, change them, etc. the drawback: it's one single object that can get very big for big XML files.
this is where SAX comes in handy. e.g. you have a (not too small) xml file and want to process it (e.g. read all elements, process them sequentially or by record). the drawback: you have to implement a event listener class to catch the events for each sequential node.
conclusion:
* use DOM for
- small XMLs
- XMLs to change and write back to a file (or another stream)
* use SAX for
- larger XML
- XMLs you want to process sequentially
example: read XML content from a URL, convert the data to create SQL statements, insert the data. if you can't be sure that you always get only small results, i would prefer SAX as you need to read each node anyway and are independent of the XML length. (it's also a memory issue).