diff --git a/packages/splitview/src/api/api.ts b/packages/splitview/src/api/api.ts
index 4c3b5ce41..dd9c79878 100644
--- a/packages/splitview/src/api/api.ts
+++ b/packages/splitview/src/api/api.ts
@@ -1,18 +1,22 @@
 import { Emitter, Event } from '../events';
 import { CompositeDisposable, IDisposable } from '../lifecycle';
 
-// anything that is serializable JSON should be valid here
-type StateObject =
+/**
+ * A valid JSON type
+ */
+export type StateObject =
     | number
     | string
     | boolean
-    | undefined
     | null
     | object
     | StateObject[]
     | { [key: string]: StateObject };
 
-interface State {
+/**
+ * A JSON-serializable object
+ */
+export interface State {
     [key: string]: StateObject;
 }
 
diff --git a/packages/splitview/src/groupview/panel/parts.ts b/packages/splitview/src/groupview/panel/parts.ts
index 5c03e955a..7d1bec17b 100644
--- a/packages/splitview/src/groupview/panel/parts.ts
+++ b/packages/splitview/src/groupview/panel/parts.ts
@@ -25,14 +25,12 @@ export interface GroupPanelPartInitParameters
 }
 
 export interface PanelHeaderPart extends IPanel {
-    id: string;
     element: HTMLElement;
     init?(parameters: GroupPanelPartInitParameters);
     setVisible(isPanelVisible: boolean, isGroupVisible: boolean): void;
 }
 
 export interface PanelContentPart extends IPanel {
-    id: string;
     element: HTMLElement;
     setVisible(isPanelVisible: boolean, isGroupVisible: boolean): void;
     init?(parameters: GroupPanelPartInitParameters);
@@ -49,7 +47,6 @@ export interface IGroupPanelInitParameters
 }
 
 export interface IGroupPanel extends IDisposable, IPanel {
-    id: string;
     header: PanelHeaderPart;
     content: PanelContentPart;
     group: IGroupview;
diff --git a/packages/splitview/src/panel/types.ts b/packages/splitview/src/panel/types.ts
index 2f9ce377b..efd62416d 100644
--- a/packages/splitview/src/panel/types.ts
+++ b/packages/splitview/src/panel/types.ts
@@ -1,15 +1,24 @@
+import { State } from '../api/api';
 import { IDisposable } from '../lifecycle';
 
+/**
+ * A key-value object of anything that is a valid JavaScript Object.
+ */
+export interface Parameters {
+    [key: string]: any;
+}
+
 export interface PanelInitParameters {
-    params: { [index: string]: any };
-    state?: { [index: string]: any };
+    params: Parameters;
+    state?: State;
 }
 
 export interface PanelUpdateEvent {
-    params: { [index: string]: any };
+    params: Parameters;
 }
 
 export interface IPanel extends IDisposable {
+    readonly id: string;
     init?(params: PanelInitParameters): void;
     layout?(width: number, height: number): void;
     update?(event: PanelUpdateEvent): void;
diff --git a/packages/splitview/src/react/baseReactComponentView.tsx b/packages/splitview/src/react/baseReactComponentView.tsx
index b88a8ebf8..d745ef557 100644
--- a/packages/splitview/src/react/baseReactComponentView.tsx
+++ b/packages/splitview/src/react/baseReactComponentView.tsx
@@ -11,7 +11,7 @@ export class BaseReactComponentGridView<T extends BaseViewApi>
     implements IPanel {
     private _element: HTMLElement;
     private part: ReactPart;
-    private params: { params: any };
+    private params: PanelInitParameters;
 
     private _onDidChange: Emitter<number | undefined> = new Emitter<
         number | undefined
@@ -66,7 +66,7 @@ export class BaseReactComponentGridView<T extends BaseViewApi>
     }
 
     update(params: PanelUpdateEvent) {
-        this.params = { ...this.params.params, ...params };
+        this.params = { ...this.params, params: params.params };
         this.part.update(params);
     }
 
diff --git a/packages/splitview/src/react/gridview/reactComponentGridView.ts b/packages/splitview/src/react/gridview/reactComponentGridView.ts
index 78cdc338a..48960e090 100644
--- a/packages/splitview/src/react/gridview/reactComponentGridView.ts
+++ b/packages/splitview/src/react/gridview/reactComponentGridView.ts
@@ -1,5 +1,5 @@
 import { ReactLayout } from '../dockview/dockview';
-import { PanelInitParameters, IPanel } from '../../panel/types';
+import { PanelInitParameters } from '../../panel/types';
 import { IGridPanelComponentView } from '../../gridview/componentGridview';
 import { FunctionOrValue } from '../../types';
 import { BaseReactComponentGridView } from '../baseReactComponentView';
diff --git a/packages/splitview/src/react/splitview/reactComponentView.ts b/packages/splitview/src/react/splitview/reactComponentView.ts
index 34a35abaf..628d159d5 100644
--- a/packages/splitview/src/react/splitview/reactComponentView.ts
+++ b/packages/splitview/src/react/splitview/reactComponentView.ts
@@ -1,7 +1,6 @@
 import { IView } from '../../splitview/splitview';
 import { ReactLayout } from '../dockview/dockview';
 import { ISplitviewPanelProps } from './splitview';
-import { IPanel } from '../../panel/types';
 import { BaseReactComponentGridView } from '../baseReactComponentView';
 import { PanelApi } from '../../api/panelApi';