How to give readmore for a text?

I am having a long text inside p tag. <p> type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum</P> i want to show a read more link if the text is greater than 100 charectors(like in whatsapp).How to implement that? whether i can do it by pur css? or js needed? it should toggle between readmore and readless.