refactor(core): Removed readonly getters and changed to readonly (#19842)

variables

PR Close #19842

packages/common/http/test/jsonp_mock.ts

@@ -23,13 +23,12 @@ export class MockScriptElement {
 
 export class MockDocument {
   mock: MockScriptElement|null;
+  readonly body: any = this;
 
   createElement(tag: 'script'): HTMLScriptElement {
     return new MockScriptElement() as any as HTMLScriptElement;
   }
 
-  get body(): any { return this; }
-
   appendChild(node: any): void { this.mock = node; }
 
   removeNode(node: any): void {
@@ -41,4 +40,4 @@ export class MockDocument {
   mockLoad(): void { this.mock !.listeners.load !(null as any); }
 
   mockError(err: Error) { this.mock !.listeners.error !(err); }
-}
+}