You could compare the original value of the field and the changed value of the field and deduct the difference as the pasted value. This catches the pasted text correctly even if there is existing text in the field.
function text_diff(first, second) {
var start = 0;
while (start < first.length && first[start] == second[start]) {
++start;
}
var end = 0;
while (first.length - end > start && first[first.length - end - 1] == second[second.length - end - 1]) {
++end;
}
end = second.length - end;
return second.substr(start, end - start);
}
$('textarea').bind('paste', function () {
var self = $(this);
var orig = self.val();
setTimeout(function () {
var pasted = text_diff(orig, $(self).val());
console.log(pasted);
});
});