http://jsfiddle.net/bobbyrne01/Lnq5mffs/
HTML
..
<input type="text" id="separator" value="Doesnt\nwork" />
<input type="button" id="button" value="submit" />
javascript
..
document.getElementById('button').onclick = function(){
alert(document.getElementById('separator').value);
alert("This\nworks");
};
Output ..
- first dialog:
- second dialog: