change user to userAdmin

[Namnika]

I found one typo in the topic optional chaining.

snippet:

let userAdmin = {
  admin() {
    alert("I am admin");
  }
};

In the below phrase:

Here, in both lines we first use the dot (userAdmin.admin) to get the admin property, because we assume that the userAdmin object exists, so it's safe read from it.

user should be userAdmin cause the obj's name is userAdmin not user.

PS: Thank you for these great docs! A lot of information are well cleared.

Closes: #3499

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