I have a need to change something within a page depending on the body tag id.

My code doesn't seem to work, can you help?

function changeHeaderTitle(){
    var bodyId = document.getElementsByTagName("body").id;
    alert(bodyId);
}

This just echoes "undefined".

I have a need to change something within a page depending on the body tag id.

My code doesn't seem to work, can you help?

function changeHeaderTitle(){
    var bodyId = document.getElementsByTagName("body").id;
    alert(bodyId);
}

This just echoes "undefined".

• javascript
• getelementbyid

• 3 Someone asks this question every day, and yet I can never find a suitable dupe. Please read the documentation! – Evan Davis Commented Jan 23, 2013 at 18:03

3 Answers 3

getElementsByTagName returns collection of nodes, even if the collection is bound to contain only one element. Try

var bodyId = document.getElementsByTagName("body")[0].id;
// select the first (and only) body:              ^^^

or better yet

var bodyId = document.body.id;

Yeah, try this:

 document.getElementsByTagName("body")[0].id

because getElementsByTagName returns an array.

document.getElementsByTagName('body')[0].id

Note that getElementsByTagName returns an array of obj