Formatting Lines In A Variable

There is a variable:

input = window.document.sidegenerate.input.value;
This variable points to a textarea of a form. Meaning that it has multiple lines.

What I want to do is have code added before and after each line. Example:

Original Input:
Line 1
Line 2
Line 3
Line 4
etc

This would be the output:
<h2>Line 1</h2>
<b>Line 2</b>
<b>Line 3</b>
<b>Line 4</b>
<b>etc</b>

As you can see, all the lines have had the same formatting added to them except for the first line. Which has different formatting.