/**
*@NApiVersion 2.0
*@NScriptType ClientScript
*/
define(["N/currentRecord"], function(currentRecord){
        var pageInit = function(context) { } //just to add an entry point

        var customSubmit = function(context) {
            var val = currentRecord.getValue({fieldId: 'field_id1'}); 
            currentRecord.setValue({fieldId: 'field_id2', value: val});
        }
    return {
            pageInit: pageInit,
        customSubmit: customSubmit
    }
});`