Array.from(document.querySelectorAll("pre code")) .forEach(function(element){ console.log(element.clientHeight ) let code = element.innerHTML; let n = document.createElement('div'); n.className = 'code'; n.innerHTML = code; n.setAttribute("height", "200px"); let par = element.parentNode; par.outerHTML = n.outerHTML; }) Array.from(document.querySelectorAll(".code")) .forEach(function(element){ let html = element.innerHTML; element.innerHTML = ''; let n = document.createElement('iframe'); n.setAttribute("style", "width: 100%; height: 200px; border: 0;") n.frameBorder = 0; element.appendChild(n); var iframeDocument = n.contentDocument; // Set the content of the iframe iframeDocument.open(); iframeDocument.write(`