![Sam Thorogood](https://web.dev/images/authors/samthorogood.jpg) Sam Thorogood [X](https://twitter.com/samthor) [GitHub](https://github.com/samthor) [Homepage](https://whistlr.info/)

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In Chrome 50, you'll be able to check the support of options for some HTML attributes that are backed by `DOMTokenList` instances in JavaScript.
Right now, these places are:

- iframe sandbox options
- link relations (the rel attribute, or relLink in JavaScript)

Let's show a quick example:

```javascript
var iframe = document.getElementById(...);
if (iframe.sandbox.supports('an-upcoming-feature')) {
    // support code for mystery future feature
} else {
    // fallback code
}
if (iframe.sandbox.supports('allow-scripts')) {
    // instruct frame to run JavaScript
    // NOTE: this is well-supported, and just an example!
}
```

As the list of supported options grows and changes, you can use feature detection to perform the correct actions for your web applications.