how to check if a tag exists using javascript without getting an error

Question

I have xml data with root "clients" and it can contains multiple elements of "client" inside it. sometimes there are no client elements that are returned in the XML file (this is ok). I need to determine if there are any client elements returned so i tried using:

if(typeof myfile.getElementsByTagName("client")){
  alert("no clients");
}

This does the intended job, but I get a firebug error whenever there are no "client" elements.

Mackay

Answer 1

Why not just check for the length of the NodeList?

if( myfile.getElementsByTagName("client").length == 0 )
{
 alert("no clients");
}

Add this to check if myfile has been defined

if( typeof myfile == "undefined" || myfile.getElementsByTagName("client").length == 0 )
{
 alert("no clients");
}

Kayne

it still makes an error message that says 'null' is not an object – Mackay

@Mackay - Is myfile null? If you run this in the console for this page if( document.getElementsByTagName("client").length == 0 ) { alert("no clients"); } it will alert "no clients". – Kayne

ok you are right. basically the file was coming in as completely empty when there were no clients. So it wasn't any longer a legit xml document. Thanks for first answer though. it helped me isolate the problem. – Mackay

@Mackay - Glad you got it figured out :) – Kayne

Answer 2

Try:

if (!myfile.getElementsByTagName("client").length) {}
//                                          ^ falsy (0) if no elements

if you're not sure myfile exists as an element you should check for that first:

if (typeof myfile !== 'undefined'
    && myfile.getElementsByTagName 
    && myfile.getElementsByTagName("client").length) {}

Corin