i want doing a project then i need something similiar like the "more" link

I have a long text but i want to display only a certain number of text if i click on the "More" this link it will appear those text that is being hide
Like those people have a very long comment, Facebook will appear a short text and it use the "More" link to display the rest of the text
So how to create using JavaScript language ?
Urgently need help in this!!!!!!!!!!!!!!!!!!!!!!!!!