how to validate the HtmlEditor using java script?

[i3class]

Hi,
I have a requirement
I want to validate HtmlEditor text using java script.
first time i entered the text and saved in DataBase.
After that again I cleared the text , now this time i wrote the below code under update button click event on listener.

if (txtPreRequisites.getValue() == "" || txtPreRequisites.getValue() == " ") {
           alert("Course prerequisites required");
 }

but its is returning <br/> so alert is not displaying.

Please help me.

Note: Screen shot attached.