Logging and asserting the number of previously-unknown DOM elements - cypress

Question

I'ts my first tme using Cypress and I almost finalized my first test. But to do so I need to assert against a unknown number. Let me explain:
When the test starts, a random number of elements is generated and I shouldn't have control on such a number (is a requirement). So, I'm trying to get such number in this way:
var previousElems = cy.get('.list-group-item').its('length');
I'm not really sure if I'm getting the right data, since I can not log it (the "cypress console" shows me "[Object]" when I print it). But let's say such line returns (5) to exemplify.
During the test, I simulate a user creating extra elements (2) and removing an (1) element. Let's say the user just creates one single extra element.
So, at the end os the test, I need to check if the number of eements with the same class are equals to (5+2-1) = (6) elements. I'm doing it in this way:
cy.get('.list-group-item').its('length').should('eq', (previousTasks + 1));
But I get the following message:
CypressError: Timed out retrying: expected 10 to equal '[object Object]1'
So, how can I log and assert this?
Thanks in advance,
PD: I also tryed:
var previousTasks = (Cypress.$("ul").children)? Cypress.$("ul").children.length : 0;
But it always returns a fixed number (2), even if I put a wait before to make sure all the items are fully loaded.
I also tryed the same with childNodes but it always return 0.

Answer 1

Your problem stems from the fact that Cypress test code is run all at once before the test starts. Commands are queued to be run later, and so storing variables as in your example will not work. This is why you keep getting objects instead of numbers; the object you're getting is called a chainer, and is used to allow you to chain commands off other commands, like so: cy.get('#someSelector').should('...');
Cypress has a way to get around this though; if you need to operate on some data directly, you can provide a lambda function using .then() that will be run in order with the rest of your commands. Here's a basic example that should work in your scenario:
cy.get('.list-group-item').its('length').then(previousCount => {
// Add two elements and remove one...
cy.get('.list-group-item').its('.length').should('eq', previousCount + 1);
});
If you haven't already, I strongly suggest reading the fantastic introduction to Cypress in the docs. This page on variables and aliases should also be useful in this case.