Migrating to IFRAME Sandbox Mode

Apps Script uses a security sandbox to provide protective isolation for G Suite applications in certain situations. All sandbox modes are now sunset except for IFRAME. Apps using older sandbox modes now use the newer IFRAME mode automatically.

Apps that previously used these older modes with the HTML Service may need to make changes for IFRAME mode, to address the following differences:

  • You now must override the link's target attribute using target="_top" or target="_blank"
  • HTML files served by the HTML Service must include <!DOCTYPE html>, <html>, and <body> tags
  • The Google native loader library api.js doesn't load automatically in IFRAME mode
  • Picker users need to call setOrigin() because content is served from a new domain
  • Some older browsers, including IE9, are not supported
  • Imported resources must now use HTTPS
  • Form submission are no longer prevented by default

These differences are detailed in the following sections.

In the IFRAME mode you need to set the link target attribute to either _top or _blank:

Code.js

function doGet() {
  var template = HtmlService.createTemplateFromFile('top');
  return template.evaluate();
}

top.html

<!DOCTYPE html>
<html>
 <body>
   <div>
     <a href="http://google.com" target="_top">Click Me!</a>
   </div>
 </body>
</html>

You can also override this attribute using the <base> tag within the head section of the enclosing web page:

<!DOCTYPE html>
<html>
  <head>
    <base target="_top">
  </head>
  <body>
   <div>
     <a href="http://google.com">Click Me!</a>
   </div>
 </body>
</html>

Top-level HTML tags

Under NATIVE (and EMULATED) sandbox mode, certain HTML tags would be automatically added to an Apps Script .html file, but this does not happen when using IFRAME mode.

To make sure your project pages are served correctly using IFRAME, wrap your page content in the following top-level tags:

<!DOCTYPE html>
<html>
  <body>
    <-- your HTML content here -->
  </body>
</html>

Native Javascript loader library must be explicitly loaded

Scripts that relied on automatic loading of the native loader library api.js must be changed to load this library explicitly, as in the following example:

<script src="https://apis.google.com/js/api.js?onload=onApiLoad">
</script>

Picker API change

When using the Picker API, you must now call setOrigin() when constructing the PickerBuilder and pass in the origin google.script.host.origin, as shown in the following example:

function createPicker(oauthToken) {
  var picker = new google.picker.PickerBuilder()
      .addView(google.picker.ViewId.SPREADSHEETS) // Or a different ViewId
      .setOAuthToken(oauthToken)
      .setDeveloperKey(developerKey)
      .setCallback(pickerCallback)
      .setOrigin(google.script.host.origin) // Note the setOrigin
      .build();
  picker.setVisible(true);
}

For a full working example, see File-open dialogs.

Browser support

The IFRAME sandbox mode is based on the iframe sandboxing feature in HTML5. This is not supported in some older browsers, such as Internet Explorer 9. This can be an issue if your Apps Script project both:

  • uses HtmlService, and
  • previously used EMULATED or NATIVE sandboxing

Migrating these apps to IFRAME sandbox mode means they may no longer work on some older browsers (notably IE9 and earlier) that don't support HTML5's iframe sandboxing feature.

Apps that already request IFRAME mode or don't use HtmlService at all are unaffected by this issue.

HTTPS is now required for imported resources

Previous applications that imported resources using HTTP must be changed to use HTTPS instead.

Form submission are no longer prevented by default

Under NATIVE sandboxing HTML forms were prevented from actually submitting and navigating the page. Given that, a developer could simply add an onclick handler to the submit button and not have to worry about what happened after.

With IFRAME mode however HTML forms are allowed to submit, and if a form element has no action attribute specified it will submit to a blank page. Worse, the inner iframe will redirect to the blank page before the onclick handler has a chance to finish.

The solution is to add JavaScript code to your page that prevents the form elements from actually submitting, so that the click handlers have time to function:

<script>
  // Prevent forms from submitting.
  function preventFormSubmit() {
    var forms = document.querySelectorAll('form');
    for (var i = 0; i < forms.length; i++) {
      forms[i].addEventListener('submit', function(event) {
        event.preventDefault();
      });
    }
  }
  window.addEventListener('load', preventFormSubmit);
</script>

A complete example can be found on the HtmlService guide Client-to-Server Communication.

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