select onChange not working inside a form

I found that as you set name and id attribute same of your function name causing this conflict and prompting error viewroom is not a function, change the name of function. also define your js at the bottom of document.

function viewRoom()
{
    alert(123);
}

Working Demo

Your function name conflicts with name and id of the select, just give another name to the function.

You can't name a function the same as an element on your page. I suggest changing the function name to something like viewroomSelected as shown here in this jsFiddle.

Relevant changes:

function viewroomSelected()
{
  alert(123);
}

<select name="viewroom" id="viewroom" onChange="viewroomSelected()">