Using jQuery to replace one tag with another

It's correct that you'll always obtain the first code's contents, because $('code').html() will always refer to the first element, wherever you use it.

Instead, you could use .each to iterate over all elements and change each one individually:

$('code').each(function() {
    $(this).replaceWith( "<pre>" + $(this).html() + "</pre>" );
    // this function is executed for all 'code' elements, and
    // 'this' refers to one element from the set of all 'code'
    // elements each time it is called.
});

You can pass a function to .replaceWith ^[docs]:

$('code').replaceWith(function(){
    return $("<pre />", {html: $(this).html()});
});

Inside the function, this refers to the currently processed code element.

DEMO

Update: There is no big performance difference, but in case the code elements have other HTML children, appending the children instead of serializing them feels to be more correct:

$('code').replaceWith(function(){
    return $("<pre />").append($(this).contents());
});

This is much nicer:

$('code').contents().unwrap().wrap('<pre/>');

Though admittedly Felix Kling's solution is approximately twice as fast:

Try this:

$('code').each(function(){

    $(this).replaceWith( "<pre>" + $(this).html() + "</pre>" );

});

http://jsfiddle.net/mTGhV/