$（var）和var有什么区别？

Question

It came to my understanding that you can use a DOM element as jQuery selector eg $(document) .
So why does the jQuery attr() function work in both these cases?

let v = $("#nodeID");
//First case
$(v).attr("href","www1"); //works
//Second case
v.attr("href","www2"); //also works

What's the difference?

Answer 1

When you pass a jQuery object to $ , it will return a jQuery object containing the same elements as in the original jQuery object you passed. They're basically the same (though the objects are not === ). You can nest jQuery objects in $ as much as you want, it won't make a difference, it's just odd to do.

 $($($('div'))).text('foo'); 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <div></div> 

Answer 2

There are many different kinds of value you can pass to the jQuery function. In this case you are passing a jQuery selection about which the documentation says:

selection
Type: jQuery
An existing jQuery object to clone.

So you are cloning var .

In this context, it is entirely pointless. (It can be useful if you were going to mutate the value but needed to preserve the original to use elsewhere).