Java and JavaScript in the Database

Hi All,
is it possible to change the format mask for a column using javascript?
I tried the following but it didn't help:
var fields = apex.region("test").call("getViews").grid.model.getOption("fields");
for(k in fields){

    fields\[k\].formatMask = "999G999G999G999G990D0000";  
 }  
  
apex.region("test").widget().interactiveGrid("getViews", "grid").view$.grid("refreshColumns");  
apex.region("test").widget().interactiveGrid("getViews", "grid").view$.grid("refresh");  

thanks