How to save user input textfield data in a variable

i want to save the user entered data from textfield into a local variable. i have tried the following code, but no value is coming from the textfield.

var u=tname.value.toString(); // tname is my textfield name var p=tpass.value.toString(); tpass is my textfield name

and i have also tried other method of textfield still not working

var u=tname.getValue(); var p=tpass.getValue();

can any one help me. how should i get this.