Why is the javascript function not called in a web page?

There are two textboxes  (txtTimeFrom and txtTimeTo)  for a time period in a webpage embed in a asp.net Master page. I used a javascript to validate the data a user enters in these two boxes as a date type on TxtTimeTo onBlur event then call TextTimeTo's code behind event TextChanged to  access SQL to get data.
The issues is the javascript is never called and TextChanged is fired directly. How to solve this issues? Thanks in advance!