<iframe src="//instagram.com/p/0123456789/embed/" width="612" height="710" frameborder="0" scrolling="no" allowtransparency="true"></iframe>
var regex = /src=['|"]//instagram.com/p/(.*?)/embed/['|"]/;
<iframe src="//instagram.com/p/0123456789/embed/" width="612" height="710" frameborder="0" scrolling="no" allowtransparency="true"></iframe>
src="[^d]+(d+)
<iframe src="//instagram.com/p/0123456789/embed/" width="612" height="710" frameborder="0" scrolling="no" allowtransparency="true"></iframe>
iframes = document.getElementsByTagName('iframe');
src = iframes[0].src;
regex = /instagram.com/p/(d*)(.*)/;
instagram_id = src.match(regex, src)[1];
src=['|"]//instagram.com/p/(.*?)/embed/['|"]