Is using document.getElementsByTagName() a good idea or bad idea?

Question

Ok so I am wondering which way is the preffered way to access a certain tag.

Is it better to use..

document.getElementById('myDiv').innerHTML

or this way..

document.getElementsByTagName('div')[0].innerHTML 
// I use [0] because it is the first div in the body

My guess is that it doesn't matter at all which way i do it.

Answer 1

Absolutely the getElementById is better in that case. It's much faster.

Update

Here is a test about JavaScript selector functions. http://jsperf.com/queryselectorall-vs-getelementbyid/6

There are not many articles about performance of JavaScript selector functions. Instead there are many articles about jQuery selector performance like this or this. jQuery uses native JavaScript selector functions internally, so you can guess from these articles.