Are what Cypress doc calls "subjects" JS generators, JS promises, regular JS objects or something else?

[JacquesRobin]

Cypress.io noob getting confused with the jargon used in the doc.

The doc says that cypress commands yield their result rather than returning them. Should I infer from that that the implicit argument that is passed through the cypress call chains is a JS Generator Function or JS Generator Object? Or do they used the word "yield" to refer to a different concept than the one denoted by the Vanilla JS keyword "yield"?

The doc seems to call this implicit argument a "subject", but it does not seem to have anything to do with the concept of subject in subject-oriented programming, nor with the concept of subject in the observer pattern, so does this choice of word does refer to another CS concept that I have never heard of?

The "then()" command seems to transform a yielded value into a returned value so that one can assign it to a variable passed as explicit argument the next command in the chain. Should I infer from that that the implicit argument that is passed through the cypress call chain is what Vanilla JS calls a Promise object?

So I am wondering whether the implicit argument called "subject" passed through the cypress command chains is:

1. a JS generator function?
2. a JS generator object?
3. a JS promise object?
4. none of the above but just a regular JS object?
5. none of the above but a special kind of JS object called, "subject" -- confusingly overloading the word already used with a different meaning in subject-oriented programming and in the observer pattern -- and, if it a special, then what are the special properties that distinguish it from a regular JS object?

Any clarification much appreciated.

[bartvdbraak]

Hello @JacquesRobin,

I understand that you're feeling confused about some of the jargon used in the Cypress.io documentation. I'll do my best to clarify the concepts for you.

In Cypress, when the documentation states that Cypress commands "yield" their result rather than returning them, it does not refer to JavaScript generator functions or objects using the yield keyword. Instead, "yield" here means that the command's result is passed to the next command in the chain for further processing.

The term "subject" in Cypress refers to the implicit argument passed through the Cypress command chains. It represents the target element or elements on which the subsequent commands will operate. In other words, the subject is the element(s) that you're interacting with using Cypress commands. It doesn't directly relate to the concept of subjects in subject-oriented programming or the observer pattern.

Regarding the then() command, it is not transforming a yielded value into a returned value in the sense of Promises. In Cypress, the then() command is used for chaining assertions or custom actions after a previous command. It allows you to perform additional operations on the subject or its result.

To answer your questions directly:

• The implicit argument called "subject" passed through the Cypress command chains is none of the options you mentioned (i.e., not a JS generator function, generator object, or Promise object).
• It is simply a regular JavaScript object representing the target element(s) of the command chain.
• The term "subject" in Cypress is used specifically within the context of Cypress commands and does not have any special properties beyond being the element(s) under test.

I hope this clarifies the concepts for you. If you have any further questions or need additional clarification, feel free to ask.