Set iframe innerHTML without loading page in it (with jquery)

I want to set the contents of an iframe dynamically, when no pages were loaded before in the iframe.

I'm doing that :

iframe = $('<iframe id="thepage"></iframe>');

iframeHtml = 'iframeHtml';
$('body').append(iframe);

iframe
.contents()
.html(iframeHtml);

But it is not working, the html is still empty.