Trusted Types Violation Fixes

[jgoping]

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have helpful link attached, see contributing.md

Documentation

There are three tsec violations that are fixed in this PR:

1. ban-element-innerhtml-assignments: maintain--tab-focus.ts

The innerHTML assignment here is unsafe as a string is being used that could contain an XSS attack. The solution chosen was to replace the string containing HTML with programmatically-created DOM elements. This removes the Trusted Types violation as there is no longer a string passed in that can contain an XSS attack.

Notes on solution:

• The <svg> tag is omitted completely since the original snippet returns fragment.firstChild.firstChild. The first firstChild omits the <div>, and the second firstChild omits the <svg>, so to remove unnecessary code the created elements start at the foreignObject level.
• The reason createElementNS is used instead of createElement is because the ‘foreignObject’ element is a separate namespace from the default HTML elements. The documentation for this command is found here.

The code was tested to be equivalent by rendering both the original code and the re-written code in a browser to see if they evaluate to the same thing in the DOM. The DOM elements styles were then compared to ensure that they were identical.

2. ban-window-stringfunctiondef: packages/next/lib/recursive-delete.ts

The setTimeout function caused a Trusted Types violation because if a string is passed in as the callback, XSS can occur. The solution to this problem is to ensure that only functions can be passed to setTimeout. There is only one call to the sleep function and it passes in numbers only, so this can be enforced without breaking the application logic. In the process of doing this, promisify has been removed and the promise has been created explicitly.

The code was tested in a sample application to ensure it behaved as expected.

3. ban-window-stringfunctiondef: packages/next/client/dev/fouc.ts

This file also uses setTimeout, so the call was wrapped in a safeSetTimeout call that specifies that the callback argument is not a string.

[uraj]

Instead of using setAttribute, you can use the standard SVGAnimatedLength API:

foreignObject.width.baseVal.value = 30;

[jgoping]

Fixed

[bjarkler]

Looks great, ship it!

[bjarkler]

Nit: Clean this comment up and add more context. E.g.

// Construct <foreignObject width="30" height="30"><input type="text"/></foreignObject>
// in a way that does not raise a Trusted Types violation.