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The iframe tag allows us to embed content coming from other origins (other sites) into our web page.

Technically, an iframe creates a new nested browsing context. This means that anything in the iframe does not interfere with the parent page, and vice versa. JavaScript and CSS do not “leak” to/from iframes.

Many sites use iframes to perform various things. You might be familiar with Codepen, Glitch or other sites that allow you to code in one part of the page, and you see the result in a box. That’s an iframe.

You create one this way:

<iframe src="page.html"></iframe>

You can load an absolute URL, too:

<iframe src="https://site.com/page.html"></iframe>

You can set a set of width and height parameters (or set them using CSS) otherwise the iframe will use the defaults, a 300x150 pixels box:

<iframe src="page.html" width="800" height="400"></iframe>

Srcdoc

The srcdoc attribute lets you specify some inline HTML to show. It’s an alternative to src, but recent and not supported in Edge 18 and lower, and in IE:

<iframe srcdoc="<p>My dog is a good dog</p>"></iframe>

Sandbox

The sandbox attribute allows us to limit the operations allowed in the iframes.

If we omit it, everything is allowed:

<iframe src="page.html"></iframe>

If we set it to “”, nothing is allowed:

<iframe src="page.html" sandbox=""></iframe>

We can select what to allow by adding options in the sandbox attribute. You can allow multiple ones by adding a space in between. Here’s an incomplete list of the options you can use:

  • allow-forms: allow to submit forms
  • allow-modals allow to open modals windows, including calling alert() in JavaScript
  • allow-orientation-lock allow to lock the screen orientation
  • allow-popups allow popups, using window.open() and target="_blank" links
  • allow-same-origin treat the resource being loaded as same origin
  • allow-scripts lets the loaded iframe run scripts (but not create popups).
  • allow-top-navigation gives access to the iframe to the top level browsing context

Allow

Currently experimental and only supported by Chromium-based browsers, this is the future of resource sharing between the parent window and the iframe.

It’s similar to the sandbox attribute, but lets us allow specific features, including:

  • accelerometer gives access to the Sensors API Accelerometer interface
  • ambient-light-sensor gives access to the Sensors API AmbientLightSensor interface
  • autoplay allows to autoplay video and audio files
  • camera allows to access the camera from the getUserMedia API
  • display-capture allows to access the screen content using the getDisplayMedia API
  • fullscreen allows to access fullscreen mode
  • geolocation allows to access the Geolocation API
  • gyroscope gives access to the Sensors API Gyroscope interface
  • magnetometer gives access to the Sensors API Magnetometer interface
  • microphone gives access to the device microphone using the getUserMedia API
  • midi allows access to the Web MIDI API
  • payment gives access to the Payment Request API
  • speaker allows access to playing audio through the device speakers
  • usb gives access to the WebUSB API.
  • vibrate gives access to the Vibration API
  • vr gives access to the WebVR API

Referrer

When loading an iframe, the browser sends it important information about who is loading it in the Referer header (notice the single r, a typo we must live with).

The misspelling of referrer originated in the original proposal by computer scientist Phillip Hallam-Baker to incorporate the field into the HTTP specification. The misspelling was set in stone by the time of its incorporation into the Request for Comments standards document RFC 1945

The referrerpolicy attribute lets us set the referrer to send to the iframe when loading it. The referrer is an HTTP header that lets the page know who is loading it. These are the allowed values:

  • no-referrer-when-downgrade it’s the default, and sends the referrer when the current page is loaded over HTTPS and the iframe loads on the HTTP protocol
  • no-referrer does not send the referrer header
  • origin the referrer is sent, and only contains the origin (port, protocol, domain), not the origin + path which is the default
  • origin-when-cross-origin when loading from the same origin (port, protocol, domain) in the iframe, the referrer is sent in its complete form (origin + path). Otherwise only the origin is sent
  • same-origin the referrer is sent only when loading from the same origin (port, protocol, domain) in the iframe
  • strict-origin sends the origin as the referrer if the current page is loaded over HTTPS and the iframe also loads on the HTTPS protocol. Sends nothing if the iframe is loaded over HTTP
  • strict-origin-when-cross-origin sends the origin + path as the referrer when working on the same origin. Sends the origin as the referrer if the current page is loaded over HTTPS and the iframe also loads on the HTTPS protocol. Sends nothing if the iframe is loaded over HTTP
  • unsafe-url: sends the origin + path as the referrer even when loading resources from HTTP and the current page is loaded over HTTPS

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