Check if WordPress Gutenberg Block Editor is ready

index.js

const { select, subscribe } = wp.data;

const closeListener = subscribe( () => {
	const isReady = select( 'core/editor' ).__unstableIsEditorReady();
	if ( ! isReady ) {
        // Editor not ready.
		return;
	}
	// Close the listener as soon as we know we are ready to avoid an infinite loop.
	closeListener();
  	// Your code is placed after this comment, once the editor is ready.
	alert( 'is ready' );
});