How to check Textbox contains any values or not?

var txt_emp_salary = document.getElementById("<%=txt_employee_salary.ClientID%>");



if(txt_emp_salary !=null)

{

   //1st way

   if(txt_emp_salary.value!= '')

   {

      alert('Textbox has a value');

   }



   //2nd way

   if(txt_emp_salary.value.length>0)

   {

      alert('Textbox has a value');

   }   

}