Okay its like this. Layers are used to separate functionality. Thats all. Javascript does not or should it EVER manage business rules! Java script is for screen interactions only (UI) The UI layer is for formatting data carried fromm the business layer only The business layer takes information from the data layer. Builds the business object and performs all business validations needed. The data layer just returns data from your data source whatever that may me text files, sql, mysql, oracle, microaprocessors, rs-232 serial input/output, etc... don't let anyone tell you different 1 line of code equals many bugs. So don't write any!!