jquery: i have to use parseInt() even when deal with numbers, why?

Answer 1

http://www.uvsc.edu/disted/decourses/mct/2760/IN/krutscjo/lessons/06/ff_05.html

Javascript treats most everything as a string unless you explicitly tell it that it is a number. One notable example of this is getting values from form elements. Depending on the browser and user input you may get some unexpected results.