How to show part of the output in italic using ('div') and CSS (JavaScript)

When I use this codes, it Prints the result in a new html page, how can I print the results in a nominated textarea? lets say I want the result to be shown in: bookForm.myText.value

Update: PLEASE NOTE ONLY THE bTitle IS SUPPOSED TO BE ITALIC

HTML:
<div contenteditable="true"></div>

CSS:
span{
font-style: italic;
}

JavaScript:
bTitle = bookForm.txtTitle.value;
bName = bookForm.txtName.value;
bNumber = bookForm.txtNumber.value;

var concatBook = "<span>"+bTitle+"</span> by "+bName+" sold "+bNumber+" Copies."
$('div').html(concatBook);

Please Note that ONLY bTitle is supposed to be italic