Using jQuery object understanding [duplicate]

Question

I had to jump into jQuery development without getting too much time into learning all the associated basics, so there is one thing that throws me off quite a bit.

I see two different ways our developers access jQuery objects:

Case 1:

var container =  $("#containerId");

// Then use it as:
container.hide();

Case 2:

var container =  $("#containerId");

// Then use it as:
$(container).hide();

From my thin up to date knowledge, by wrapping a container as in var obj = $(container), we get a jQuery object obj that we can further work with.

But then why do I see intermittently developers wrapping it again when using as in $(obj).doSomething()?

Edit: the question suggested as duplicate is asking about best practices and although similar, my question is purely on understanding of jQuery object wrapping.

Answer 1

Second wrapping does nothing as I remember. So if there can be a selector a dom element or a jQuery object you can just wrap it and do not care about what it was.

But if you know it is a jquery object, you shouldn't use wrapping.

Answer 2

When developers develop a function, for example in a jQuery plugin, that can get a parameter that is either a DOM element or a jQuery object or a selector, then they use it:

function x(container) {
    container = $(container);
    // use container as a jquery object
}

// these both work:
x("#containerId");
x($("#containerId"));
x(document.getElementById("containerId"));