Question

I want to add iframe element to the page and then add <p> element inside that iframe.
I tried this:

var iframe = document.createElement('iframe');
iframe.frameBorder = 1;
iframe.width = "500px";
iframe.height = "250px";
iframe.id = "iframe";

var p = document.createElement('p');
iframe.appendChild(p);
document.getElementById("div").appendChild(iframe); //this is a div  that I have in body.

The iframe is added to the page but P is not added into iframe(iframe’s body)

Answer 1

In modern browsers, you use the contentDocument attribute. In others, you have to use contentWindow.document. You create the paragraph using the iframe’s document, in the onload event. So:

var iframe = document.createElement('iframe');
iframe.frameBorder = 1;
iframe.width = "500px";
iframe.height = "250px";
iframe.id = "iframe";

iframe.onload = function()
{
    var doc = iframe.contentDocument || iframe.contentWindow.document;
    var p = doc.createElement('p');
    p.textContent = "Paragraph in iframe";
    doc.body.appendChild(p);
};

document.getElementById("div").appendChild(iframe); //this is a div  that I have in body.

I made a jsfiddle demo.

Also, I recommend you don’t use ids that are the same as the tag name. It could become confusing.