Html, Set Iframe Src As A Javascript Variable

I would like to display a window in my webpage of another webpage, hopefully via iframe. I need to set the src as a javascript variable, here is the code:

Solution 1:

Try this:

var URLis = document.URLframe.Dest.value;
document.write('<center><iframe src="' + URLis + '" width=1350 height=500 seamless></center>');