WordPress check Gutenberg editor is ready

gutenberg-helpers.js

import { select, subscribe } from '@wordpress/data'

export function whenEditorIsReady() {
    return new Promise((resolve) => {
        const unsubscribe = subscribe(() => {
            // This will trigger after the initial render blocking, before the window load event
            // This seems currently more reliable than using __unstableIsEditorReady
            if (select('core/editor').isCleanNewPost() || select('core/block-editor').getBlockCount() > 0) {
                unsubscribe()
                resolve()
            }
        })
    })
}