Desktop, Mobile: Improve focus handling

packages/lib/utils/focusHandler.ts

@@ -0,0 +1,41 @@
+// The purpose of this handler is to have all focus/blur calls go through the same place, which
+// makes it easier to log what happens. This is useful when one unknown component is stealing focus
+// from another component. Potentially it could also be used to resolve conflict situations when
+// multiple components try to set the focus at the same time.
+
+import Logger from '@joplin/utils/Logger';
+
+const logger = Logger.create('setFocus');
+
+enum ToggleFocusAction {
+	Focus = 'focus',
+	Blur = 'blur',
+}
+
+interface FocusableElement {
+	focus: ()=> void;
+	blur: ()=> void;
+}
+
+const toggleFocus = (source: string, element: FocusableElement, action: ToggleFocusAction) => {
+	if (!element) {
+		logger.warn(`Tried action "${action}" on an undefined element: ${source}`);
+		return;
+	}
+
+	if (!element[action]) {
+		logger.warn(`Element does not have a "${action}" method: ${source}`);
+		return;
+	}
+
+	logger.debug(`Action "${action}" from "${source}"`);
+	element[action]();
+};
+
+export const focus = (source: string, element: any) => {
+	toggleFocus(source, element, ToggleFocusAction.Focus);
+};
+
+export const blur = (source: string, element: any) => {
+	toggleFocus(source, element, ToggleFocusAction.Blur);
+};