Resolve data in custom command

Description I cannot find a way to resolve data in a custom command, using a Cypress.Promise.

Code In support/commands

Cypress.addParentCommand('signIn', function (email, password) {
  return new Cypress.Promise((resolve, reject) => {
    cy.request({
      method: 'POST',
      url: '/auth',
      body: {email, password}
    })
    .then(result => {
      resolve(result.body);
    }, reject)
  });
});

In my test:

describe('any test', function () {
  it('should work', function() {
    cy.signIn('[e-mail]', 'password')
     .then(res => console.log(res))
  });
});

When I return the promise like above, cy.signIn times out. It does not fail when I do not return the promise, but I still can’t access the request data. Am I doing anything wrong?

[ChristophP]

We also had problems with returning values from custom commands. It took us a while to find this thread about cy.chain(). Our commands are working now. @brian-mann could you please update the docs for the chain method because I couldn’t find it in the docs. I would like to understand how it works specifically.

[brian-mann]

Ah okay the reason this is happening is due to the way Cypress chaining works - there are rules about parent > child commands which ultimately resets the subject between new ‘chains’. It makes sense in the general API but when writing custom commands this is basically a hidden landmine.

You need to do this…

Cypress.addParentCommand('signIn', function (email, password) {
  // chain onto the existing sets so that the subject
  // is not reset when attempting to consume the subject
  // from this custom command
  return cy.chain()
  .request({
    method: 'POST',
    url: '/auth',
    body: {email, password}
  })
  // this changes the subject to the body property from the cy.request object
  .its("body")
});