iframe without an src attribute

Question

I would like to create an <iframe> on the page, but then add the src later. If I make an iframe without an src attribute, then it loads the current page in some browsers. What is the correct value to set for the src so that it just loads a blank iframe?

The answers I've seen are:

• about:blank
• javascript:false
• javascript:void(0)
• javascript:"";
• url to a blank page

Is there a clear winner? If not, what are the tradeoffs?

I'd like to not have mixed content warnings for HTTPS urls, nor any back-button, history, or reload weirdness in all browsers from IE6 onward.

• Pekka: possible duplicate of iFrame src something other than javascript:false but same effect
• Ioannis Karadimas: You could create the iframe at the moment you have the src available, to avoid this issue. Would that work?
• Paul Tarjan: That question was asking for prettier way to write "javascript:false". I don't care how ugly the line is, I want the functionality. And the accepted answer was a url to a blank page which pays an HTTP round-trip which seems worse than being able to avoid that.
• Paul Tarjan: @Ioannis no, it is a long story, but assume I need the iframe on the page, then the url will be populated later.

Answer 1

Not sure if all browsers support "about:blank", so I'd just go with your own blank page then.

Another idea: Why not add the whole iframe using javascript instead of just the src?

• Paul Tarjan: For your first answer, that pays an unnecessary HTTP round trip, which seems sub-optimal.
• Pekka: @Paul but the second answer is spot on if you're planning to populate the iframe using js
• Paul Tarjan: For your second answer, I'm populating the iframe with form submit. So I want the iframe on the page, and then the <form> sets the src.

Answer 2

Standard approach when creating an "empty" iframe (as an iframe shim, for example), is to set the src as javascript:false;. This is the method used by most of the JavaScript libraries that create iframe shims for you (e.g. YUI's Overlay).

• rgripper: Yes, in IE9-10 iframe writes text "javascript:false;". In this case it's better to check and use src="" if not IE or if IE > 9. For IE9 - well, bad luck. PS "javascript:'';" works everywhere but calls onload twice in some browsers.
• Leigh McCulloch: This may work in all browsers but will break if a website does not allow inline javascript in their Content-Security-Policy header. Therefore please don't use this in scripts that you expect other parties to include in their sites.
• James Moberg: I agree w/@LeighMcCulloch. I've enabled CSP and javascript:false is being reported as an unsafe script-src directive when using Facebook SDK. (I believe that about:blank may be the preferred method to use.)

Answer 3

What about

about:blank

• Ioannis Karadimas: Tested in IE7,8(+quirks mode), FF3.6, Opera 10.63, Safari 5, Chrome 7.0.x - About:blank presents the most consistent behavior.
• Pekka: It's not part of a standard though so, like javascript:, you can't rely on every client interpreting it correctly
• Paul Tarjan: Mostly good testing. Still missing IE 6, FF 3, Safari 4, Chrome 5 and Chrome 6. And could OS matter here?
• Dan: What about Konqueror, @IoannisKaradimas? My point is, if it's not in the standard, you can't assume that every user will see it correctly.

Answer 4

Re your comment clarifying that you're planning to use the iframe as the target for a form submission:

I would use an empty document on the server that sends back a 204 no content.

It avoids

• "mixed content" warnings in IE and HTTPS mode
• Unnecessary errors because a client doesn't understand the javascript: protocol
• and other exotic shenanigans.

It's also valid HTML.

So what if it generates an extra request? Set the caching headers right, and there will be only one request for each client.

• Paul Tarjan: The empty document is a possibility but I would much prefer to avoid it if possible. One less thing to maintain. If the community can provide a solution that does everything the empty document does AND doesn't require the extra file, that is strictly better in my mind.
• Pekka: @Paul I agree, such a solution would be perfect. But I have seen this question a number of times on SO, and it never came up. The best there seems to be is about:blank which works in most browsers
• siannopollo: Adding the 204 status code will not trigger the onload event to be fired on the iframe in some browsers, so this may not be the best approach if someone is looking to hook into that event.

Answer 5

javascript:false:
IE10 and FF (checked in v23 in Linux) will show 'false' as content.

javascript:void(0) && javascript:;:
IE will show 'cannot display the webpage' error in the iframe. Also, when setting the src from a valid url to javascript:void(0), the page will not get blank.

about:blank:
Works in all browsers but IE 9 sends an request to the server with path "null". Still the best bet IMO

Checkout http://jsfiddle.net/eybDj/1
Checkout http://jsfiddle.net/sv_in/gRU3V/ to see how iframe src changes on dynamic updation with JS

Answer 6

javascript:false works in modern browsers.

What I've seen is that this only "fails" when dumb spiders try to load javascript:false as a page.

Solution: Block the dumb spiders.

• Martijn Pieters: There will always be more dumb spiders, though.
• Leigh McCulloch: This may work in all browsers but will break if a website does not allow inline javascript in their Content-Security-Policy header. Therefore please don't use this in scripts that you expect other parties to include in their sites.

Answer 7

As I posted in this question: Is an empty iframe src valid?, it looks acceptable to just leave out the src= attribute completely.

Answer 8

IMO: if you don't put the src, your page won't validate. But's about it. If you put a src="", your server will log many 404 errors.

Nothing is really wrong as in "damaging". But then, is it actually not wrong to use an iframe in itself?

°-

Answer 9

Yes, I know I'm reviving an old thread. Sue me. I'm interested in the answer.

I don't understand why having the trigger being a form submit precludes dynamically creating the IFrame. Does this not do exactly what you want?

<html>
<head>
<script type="text/javascript">
function setIFrame(elemName, target, width, height) {
 document.getElementById(elemName).innerHTML="<iframe width="+width+" height="+height+" src='"+target+"'></iframe>";
}
</script>
</head>
<body>
<div id="iframe" style="width:400px; height:200px"></div>
<form onSubmit="setIFrame('iframe', 'http://www.google.com', 400, 200); return false;">
<input type="submit" value="Set IFrame"/>
</form>
</body>
</html>

• Crescent Fresh: The OP has stated that the iframe must be created some time before its src will be known (see comment history to the question itself).
• TRiG: Don't apologise for answering old questions.

Answer 10

I run into this line of code:

iframe.setAttribute("src", "javascript:false");

as well. I wanted to remove javascript:URL.

Found this note from the Web Hypertext Application Technology Working Group [Updated 2 October 2019]

[https://html.spec.whatwg.org/multipage/iframe-embed-object.html#the-iframe-element][4.8.5_The_iframe_element]

The otherwise steps for iframe or frame elements are as follows:

If the element has no src attribute specified, or its value is the empty string, let url be the URL "about:blank".