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perf(forms): defer element.focus() to next animation frame #68884

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perf(forms): defer element.focus() to next animation frame #68884

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25 changes: 23 additions & 2 deletions packages/forms/signals/src/directive/form_field.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -152,9 +152,30 @@ export class FormField<T> {
: undefined) as NativeFormControl;

/**
* Current focus implementation, set by `registerAsBinding`.
* Focuses the host element, deferred to the next animation frame.
*
* We defer focus() to the next rAF because calling it synchronously can force
* the browser to immediately flush any pending style recalc and layout tree
* updates, which is expensive. By the time a rAF callback runs, the browser
* has already completed its normal pre-paint lifecycle for that frame (style,
* layout tree, geometry), so focus() finds a clean document and runs cheaply.
*
* The typeof guard is a safety check for server-side rendering environments
* (Node.js) and test environments (Jest/JSDOM) where requestAnimationFrame is
* not available. In those cases we fall back to calling focus() synchronously,
* since there is no rendering pipeline to optimize against anyway.
*/
private focuser = (options?: FocusOptions) => this.element.focus(options);
private focuser = (options?: FocusOptions) => {
if (typeof requestAnimationFrame === 'function') {
requestAnimationFrame(() => {
this.element.focus(options);
});
} else {
// Fallback for SSR and test environments: focus synchronously since
// there is no browser rendering pipeline to defer into.
this.element.focus(options);
}
};

/** Any `ControlValueAccessor` instances provided on the host element. */
private readonly controlValueAccessors = inject(NG_VALUE_ACCESSOR, {optional: true, self: true});
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