[Salesforce / RemoteAction] Using Date fields on a RemoteAction (PITA ALERT!)

I've just come through a bug on the Date field handling for Visual Force @RemoteAction.

We want to pass to a remote action a list of SObjects to be handled correctly.

This is the controller that hosts the @RemoteAction method:

public class MyController(){
   @RemoteAction
   public String doAction(List<contact> contacts){
      return 'All is ok!';
   }
}

This is the JS on the VF page:

function action(){
   var contact1 = {"LastName":"Smith",
                   "FirstName":"John",
                   "Phone" : "999-999-999"};
   var contact2 = {"LastName":"Brown",
                   "FirstName":"Mike",
                   "Phone" : "123-456-789"};
   var contactList= [contact1, contact2];
   Visualforce.remoting.Manager.invokeAction(
              '{!$RemoteAction.MyController.doAction}', 
              accList || [],
                function(result, event){
                    if(event.status){
                        alert(result);
                    }else{
                        //generic event error
                        alert(event.message);
                    }
                },{escape: false, timeout: 120000});
}

This runs perfectly.

But let's add a Date field on the JS part:

function action(){
   var contact1 = {"LastName":"Smith",
                   "FirstName":"John",
                   "BirthDate":"1980-01-01",
                   "Phone" : "999-999-999"};
   var contact2 = {"LastName":"Brown",
                   "FirstName":"Mike",
                   "BirthDate":"1982-11-21",
                   "Phone" : "123-456-789"};
   var contactList= [contact1, contact2];
   Visualforce.remoting.Manager.invokeAction(
              '{!$RemoteAction.MyController.doAction}', 
              contactList || [],
                function(result, event){
                    if(event.status){
                        alert(result);
                    }else{
                        //generic event error
                        alert(event.message);
                    }
                },{escape: false, timeout: 120000});
}

And all messes up, stating that you are passing an incorrect type to MyController.doAction(List).

The problem is related to how the Date type serialization is done when invoking the Remote Action (it is apparently a bug not fixed yet).

The solution is to pass a serialized version of the JS array and deserialize it with Apex:

public class MyController(){
   @RemoteAction
   public String doAction(String serializedContacts){
      List<contact> contacts = (List<contact>)JSON.deserialize(objList,List<contact>.class);
      return 'All is ok!';
   }
}

function action(){
   var contact1 = {"LastName":"Smith",
                   "FirstName":"John",
                   "BirthDate":"1980-01-01",
                   "Phone" : "999-999-999"};
   var contact2 = {"LastName":"Brown",
                   "FirstName":"Mike",
                   "BirthDate":"1982-11-21",
                   "Phone" : "123-456-789"};
   var contactList= [contact1, contact2];
   Visualforce.remoting.Manager.invokeAction(
              '{!$RemoteAction.MyController.doAction}', 
              JSON.stringify(contactList || []),
                function(result, event){
                    if(event.status){
                        alert(result);
                    }else{
                        //generic event error
                        alert(event.message);
                    }
                },{escape: false, timeout: 120000});
}

Remember: don't mess with JSON serialization!