Date validation for custom field - SuiteCRM Version 7.10.4 Sugar Version 6.5.25 (Build 344)

I have created two fields in my_custom_module called: start_date_c & end_date_c with date datatype

These fields are not mandatory fields however when i enter data into the leaving_date_c field I would like to make it is not less than join_date_c

I have tried the following:

but as i am new to SuiteCRM, i am not able to find positive response. please let me know what i m missing

i have tried the following
in custom\modules\Users\metadata\editview.dfs
i have added the following code under the field array

'displayParams' =>
    array (
         'javascript' => 'onblur => "checkStatusOption(this)"',

and following code in userEditView.js

function checkStatusOption(e) {
alert if leaving date is less than join date}

I don’t really know, never tried this, but I see there is a different method in those posts, the Callback method. Care to try that one? It looks cleaner, although none of these posts detail completely how to implement it, you’ll have to do some more Googling, I guess.

Good luck and tell us if you get it to work. Thanks