chore: refactor code to be compatible with es2022

material-web-copybara · copybara-github · commit 70a1d8e59a12 · 2025-08-13T12:55:39.000-07:00
PiperOrigin-RevId: 794698100
diff --git a/labs/behaviors/element-internals.ts b/labs/behaviors/element-internals.ts
@@ -68,7 +68,11 @@ export function mixinElementInternals<T extends MixinBase<LitElement>>(
       return this[privateInternals];
     }
 
-    [privateInternals]?: ElementInternals;
+    // In preparation for ES2022, we need to declare this property to guard
+    // against the base class calling [internals] in its constructor prematurely
+    // setting this field. Without declare, once this field is defined, it would
+    // initialize to undefined and `attachInternals()` could be called again.
+    declare [privateInternals]?: ElementInternals;
   }
 
   return WithElementInternalsElement;

Original file line number	Diff line number	Diff line change
`@@ -68,7 +68,11 @@ export function mixinElementInternals<T extends MixinBase<LitElement>>(`
`68`	`68`	`return this[privateInternals];`
`69`	`69`	`}`
`70`	`70`
`71`		`- [privateInternals]?: ElementInternals;`
	`71`	`+ // In preparation for ES2022, we need to declare this property to guard`
	`72`	`+ // against the base class calling [internals] in its constructor prematurely`
	`73`	`+ // setting this field. Without declare, once this field is defined, it would`
	`74`	+ // initialize to undefined and `attachInternals()` could be called again.
	`75`	`+ declare [privateInternals]?: ElementInternals;`
`72`	`76`	`}`
`73`	`77`
`74`	`78`	`return WithElementInternalsElement;`