nested-iframe-issues

An example of nested iframes and the issues this legacy technique can cause and hacks to work around them.

Includes:

• iOS safari scrolling
• aggressive caching in Firefox and IE
• scroll jumping when using select box

If you see issues make a pull request or prove to me I should remove the repo.

What is a nested iframe?

An iframe in content that is loaded by an iframe.

What is in this repo?

A series of phtml files! Why? Because the ipad seems to aggressively cache iframe content and I got bored trying to clear that cache. Even with it plugged into a mac and specifically setting empty cache/ignore cache etc, it loaded the cached iframe content. I could change the index page content and the iframe content and only the index page updated.

I have wrapped the iframes in divs because I didn't want to assume the iframe would be the only thing in the body.

I have nested content 4 iframes down.

Scrolling in iOS: Is this seriously a problem?

Scrolling an iframe in iOS Safari has a commonly known workaround which works fine. Unfortunately this stops working when you find yourself nested in multiple iframe layers.

This is clearly not good application design, but that is not the point of this example. At the time this application was created, it was probably a great idea (originally used framesets btw).

tl;dr

You must wrap an iframe in a div or similar and set overflow: auto and -webkit-overflow-scrolling: touch on that container. This needs to be set on every container down through your nested iframes, all the way to the container that contains the iframe that loads the content you wish to scroll.

Weirdly, you don't need to set it on the top level container! Boom. Have that in the face.

You want to read more, OK here is some more

iframe auto sizing

In a standards based (real) browser, an iframe body scrolls. In the joke that is iOS safari an iframe will automatically calculate it's height based on the content loaded inside it. This will make your body/container height change and possibly (definitely) fuck up the layout of your application.

Because of the wide use of iPads now, and the fact that Apple have forced all apps to use Safari under the hood, assholes, we now have to cater for their shit poor browser which is, relatively, worse than developing for IE6 when Chrome and Firefox were steaming ahead. I remember. I was there.

I will leave you to speculate why Apple would want to contribute to making web application development suck. No I won't. It's because they are greedy and want you to make an iPad app instead.

Anyway, this poor behaviour from Apple means that the parent element must take over the scrolling, since your iframe will now be behaving like a div.

Not only this, but any nested iframes will require that pattern to be followed all the way through the nesting.

top
|_div <- note, you don't seem to need it here
  |_iframe
    |_window
      |_div `overflow: auto; -webkit-overflow-scrolling: touch;`
        |_iframe
          |_window
            |_div `overflow: auto; -webkit-overflow-scrolling: touch;`
              |_iframe
                |_window <- you want scrolling here

nested iframe scrollbars

If you set an iframe to be 100% height of the body, you will see scroll bars.

An iframe is by default an inline element. I cannot think of a single reason why except because of the HTML4 spec.

It is an inline replaced element though, so like an img tag and unlike a span, it can have a width and height set on it. This has caught me out so often.

Unfortunately this means it has a line, 4px in Chrome. This means we get a whole stack of scrollbars, all trying to allow the 4px. If you set display: block on the iframe the scroll bars will disappear. You could set overflow: hidden on the top body, however this doesn't seem to work in the nested iframes.

If an iframe contains (an iframe contains an iframe) that needs to scroll, setting block on any of the nested 'container' iframes will stop the the scroll working. Just try setting it on either nested-iframe{1,2}.phtml layouts. Again, just like overflow rules, this doesn't seem to apply to the index layout (the top).

So, we can't use display: block, overflow: hidden or margin-bottom: -4px.

line-height: 0 on the container doesn't work because of a minimum line height so that's no use.

font-size: 0 on the container works for the scroll bars but breaks the scrolling.

The fix we found in the end was to set font-size: 1px on the iframe containers.

iframe caching in Firefox and IE

How to replicate

• Create an iframe with a src attribute pointing to content in an existing iframe content.
• Dynamically change the src property of the new nested iframe by clicking a button.
• Reload the parent iframe that it is nested inside.
• The contents remain i.e. the content assigned dynamically via the src property is reloaded, not the src specified in the attribute in the HTML page.

The solution

I tried setting headers in meta tags. The surefire way of fixing this is to not set the src attribute of the iframe, rather, set the src property. Unfortunately this has to be done with javascript in a script tag directly underneath the iframe element. It cannot be async as we need to set the property before the page renders, so any code in the dynamic content will not run.

scroll jumping in iOS

• Scroll to the bottom of the content.
• Tap the select menu
• Observe that the scroll jumps upward.

The solution

I have not found a solution for this one yet.