Get html content of a selector ( .html() ) with jQuery from a JavaScript variable that contains HTML

code variable it's just a string for your document. If you have parsed this HTML code inside the body then you can use $('#my_code'), otherwise it's still just a string so.. that's another story.

Check the other story here: http://jsfiddle.net/NSCQh/1/

I strongly suggest you have a look at jQuery's selector overview. They are the most important part of the jQuery magic, and without understanding them you'll get nowhere in the long run.

var html = $('#my_code').html()

or because that div containts text only

var txt = $('#my_code').text()

You've got a string, you need a DOM element. From that, you can get the jQuery object.

var el = document.createElement('div');
el.innerHTML = code;
console.log($(el));

pass the string to jquery and it works

var foo = '<div id="foo"> <span class="bar">fooBar</span> </div>';
var inside = $(foo).find('.bar').text();
alert(inside);

Create an ELEMENT, say p.

Use the following

$('<p>').append(code).find('div#my_code').html();

It create a p element, then append the content of variable code, then find div with id=my_code and select it's innerHTML.

Working model in the snippet.

var code = `<style type="text/css">
#example{
border:1px;
font-size:20px;
}
</style>
<div id="ex"> Some Content </div>
<div id="ex2"> Some Content <span> Another Content</span></div>
<div id="my_code">This Is My Code.</div><div id="ex3> Etc Etc </div>`;

var elm=$('<p>').append(code).find('div#my_code').html();

console.log(elm);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>