diff --git a/src/vs/workbench/api/browser/mainThreadDocumentsAndEditors.ts b/src/vs/workbench/api/browser/mainThreadDocumentsAndEditors.ts
index 575e7448869..804349ee484 100644
--- a/src/vs/workbench/api/browser/mainThreadDocumentsAndEditors.ts
+++ b/src/vs/workbench/api/browser/mainThreadDocumentsAndEditors.ts
@@ -306,7 +306,7 @@ export class MainThreadDocumentsAndEditors {
 
 	private readonly _toDispose = new DisposableStore();
 	private readonly _proxy: ExtHostDocumentsAndEditorsShape;
-	private _textEditors = <{ [id: string]: MainThreadTextEditor }>Object.create(null);
+	private readonly _textEditors = new Map<string, MainThreadTextEditor>();
 
 	private _onTextEditorAdd = new Emitter<MainThreadTextEditor[]>();
 	private _onTextEditorRemove = new Emitter<string[]>();
@@ -368,16 +368,16 @@ export class MainThreadDocumentsAndEditors {
 			const mainThreadEditor = new MainThreadTextEditor(apiEditor.id, apiEditor.editor.getModel(),
 				apiEditor.editor, { onGainedFocus() { }, onLostFocus() { } }, this._modelService);
 
-			this._textEditors[apiEditor.id] = mainThreadEditor;
+			this._textEditors.set(apiEditor.id, mainThreadEditor);
 			addedEditors.push(mainThreadEditor);
 		}
 
 		// removed editors
 		for (const { id } of delta.removedEditors) {
-			const mainThreadEditor = this._textEditors[id];
+			const mainThreadEditor = this._textEditors.get(id);
 			if (mainThreadEditor) {
 				mainThreadEditor.dispose();
-				delete this._textEditors[id];
+				this._textEditors.delete(id);
 				removedEditors.push(id);
 			}
 		}
@@ -448,16 +448,16 @@ export class MainThreadDocumentsAndEditors {
 		return undefined;
 	}
 
-	findTextEditorIdFor(editor: IWorkbenchEditor): string | undefined {
-		for (const id in this._textEditors) {
-			if (this._textEditors[id].matches(editor)) {
+	findTextEditorIdFor(inputEditor: IWorkbenchEditor): string | undefined {
+		for (const [id, editor] of this._textEditors) {
+			if (editor.matches(inputEditor)) {
 				return id;
 			}
 		}
 		return undefined;
 	}
 
-	getEditor(id: string): MainThreadTextEditor {
-		return this._textEditors[id];
+	getEditor(id: string): MainThreadTextEditor | undefined {
+		return this._textEditors.get(id);
 	}
 }
diff --git a/src/vs/workbench/api/browser/mainThreadEditors.ts b/src/vs/workbench/api/browser/mainThreadEditors.ts
index 25f4a8e1e9c..c63aa1bb7a6 100644
--- a/src/vs/workbench/api/browser/mainThreadEditors.ts
+++ b/src/vs/workbench/api/browser/mainThreadEditors.ts
@@ -160,52 +160,58 @@ export class MainThreadTextEditors implements MainThreadTextEditorsShape {
 	}
 
 	$trySetSelections(id: string, selections: ISelection[]): Promise<void> {
-		if (!this._documentsAndEditors.getEditor(id)) {
+		const editor = this._documentsAndEditors.getEditor(id);
+		if (!editor) {
 			return Promise.reject(disposed(`TextEditor(${id})`));
 		}
-		this._documentsAndEditors.getEditor(id).setSelections(selections);
+		editor.setSelections(selections);
 		return Promise.resolve(undefined);
 	}
 
 	$trySetDecorations(id: string, key: string, ranges: IDecorationOptions[]): Promise<void> {
 		key = `${this._instanceId}-${key}`;
-		if (!this._documentsAndEditors.getEditor(id)) {
+		const editor = this._documentsAndEditors.getEditor(id);
+		if (!editor) {
 			return Promise.reject(disposed(`TextEditor(${id})`));
 		}
-		this._documentsAndEditors.getEditor(id).setDecorations(key, ranges);
+		editor.setDecorations(key, ranges);
 		return Promise.resolve(undefined);
 	}
 
 	$trySetDecorationsFast(id: string, key: string, ranges: number[]): Promise<void> {
 		key = `${this._instanceId}-${key}`;
-		if (!this._documentsAndEditors.getEditor(id)) {
+		const editor = this._documentsAndEditors.getEditor(id);
+		if (!editor) {
 			return Promise.reject(disposed(`TextEditor(${id})`));
 		}
-		this._documentsAndEditors.getEditor(id).setDecorationsFast(key, ranges);
+		editor.setDecorationsFast(key, ranges);
 		return Promise.resolve(undefined);
 	}
 
 	$tryRevealRange(id: string, range: IRange, revealType: TextEditorRevealType): Promise<void> {
-		if (!this._documentsAndEditors.getEditor(id)) {
+		const editor = this._documentsAndEditors.getEditor(id);
+		if (!editor) {
 			return Promise.reject(disposed(`TextEditor(${id})`));
 		}
-		this._documentsAndEditors.getEditor(id).revealRange(range, revealType);
+		editor.revealRange(range, revealType);
 		return Promise.resolve();
 	}
 
 	$trySetOptions(id: string, options: ITextEditorConfigurationUpdate): Promise<void> {
-		if (!this._documentsAndEditors.getEditor(id)) {
+		const editor = this._documentsAndEditors.getEditor(id);
+		if (!editor) {
 			return Promise.reject(disposed(`TextEditor(${id})`));
 		}
-		this._documentsAndEditors.getEditor(id).setConfiguration(options);
+		editor.setConfiguration(options);
 		return Promise.resolve(undefined);
 	}
 
 	$tryApplyEdits(id: string, modelVersionId: number, edits: ISingleEditOperation[], opts: IApplyEditsOptions): Promise<boolean> {
-		if (!this._documentsAndEditors.getEditor(id)) {
+		const editor = this._documentsAndEditors.getEditor(id);
+		if (!editor) {
 			return Promise.reject(disposed(`TextEditor(${id})`));
 		}
-		return Promise.resolve(this._documentsAndEditors.getEditor(id).applyEdits(modelVersionId, edits, opts));
+		return Promise.resolve(editor.applyEdits(modelVersionId, edits, opts));
 	}
 
 	$tryApplyWorkspaceEdit(dto: WorkspaceEditDto): Promise<boolean> {
@@ -214,10 +220,11 @@ export class MainThreadTextEditors implements MainThreadTextEditorsShape {
 	}
 
 	$tryInsertSnippet(id: string, template: string, ranges: readonly IRange[], opts: IUndoStopOptions): Promise<boolean> {
-		if (!this._documentsAndEditors.getEditor(id)) {
+		const editor = this._documentsAndEditors.getEditor(id);
+		if (!editor) {
 			return Promise.reject(disposed(`TextEditor(${id})`));
 		}
-		return Promise.resolve(this._documentsAndEditors.getEditor(id).insertSnippet(template, ranges, opts));
+		return Promise.resolve(editor.insertSnippet(template, ranges, opts));
 	}
 
 	$registerTextEditorDecorationType(key: string, options: IDecorationRenderOptions): void {