Cypress.io: parse iframe content

cypress.js

Cypress.Commands.add('iframe', {
    prevSubject: 'element',
}, $iframe => {
    const contentWindow = $iframe.prop('contentWindow');

    return new Promise(resolve => {
        if (contentWindow && contentWindow.document.readyState === 'complete') {
            resolve(contentWindow);
        } else {
            $iframe.on('load', () => {
                resolve(contentWindow);
            });
        }
    });
});
Cypress.Commands.add('getInDocument', {
    prevSubject: 'document',
}, (document, selector) => Cypress.$(selector, document));

Usage:

cy.get('#foo > iframe').iframe().its('document').getInDocument('#bar');