Failed to execute 'appendChild' on 'Node'

// generate sandboxed iframe
	var vbody = document.appendChild(document.createElement('body'));
	var frame = vbody.appendChild(document.createElement('iframe'));

Uncaught DOMException: Failed to execute 'appendChild' on 'Node': Only one element on document allowed.

An error is occur when using the polyfill.

[SivanMehta]

@shtse8 Do you happen to know how or why flags=gated fixed this issue? I would like to avoid this issue in the future, but am unsure about blindly copying a querystring to fix the problem.

[JakeChampion]

@rpokrovskij That is because you are using the always flag, not all polyfills work in all browsers but with the always flag you are asking for all polyfills to be served to all browsers. If you want to use always flag you should combine it with the gated flag to ensure that polyfills do not run on browsers which do not require them. E.G. https://polyfill.io/v3/polyfill.js?flags=always,gated&features=Element.prototype.closest%2CElement.prototype.classList%2CElement.prototype.matches

What was the full polyfill.io url you used and what was the browser you tested on and it’s full user-agent string?