HTML email with Javascript [closed]
I don't think that is possible in an email, nor should it be. There would be major security ramifications.
Agree completely with Bryan and others.
Instead, consider using multiple sections in your email that you can jump to using links and anchors (the 'a' tag). I think that you can emulate the behavior you want by including multiple copies of the text further down in your email. This is a bet messy though, so you could just have sets of anchors that link to each other and allow you to move back in forth between the 'summary' section and the 'expanded' one.
Example:
<a href="#section1">Jump to section!</a><p>A bunch of content</p><h2 id="section1">An anchor!</h2>Clicking on the first link will move focus to the sub-section.
Do not depend on this. Any good mail client will not support executable code within an email. Any knowledgeable user will not use a client that does.