Allow URLs to be assigned to src property of HTMLImageElement

[TimvdLippe]

Running the following code in Chrome and Firefox will be successful (wasn't able to verify what Safari does):

let image = document.createElement('img');
image.src = new URL("http://google.com");
console.log(image.src);

I initially wanted to report to TypeScript that this doesn't typecheck (it reports Type 'URL' is not assignable to type 'string'.(2322)), until I discovered that the HTML spec itself doesn't allow for URL assignment: https://html.spec.whatwg.org/multipage/embedded-content.html#dom-img-src and it is a USVString (https://heycam.github.io/webidl/#idl-USVString). I am not deeply familiar with these contents, but as I understand the terminology, URL assignment would not be allowed.

Can we update the spec to allow for URLs to be assigned to the src property of an HTMLImageElement?

[domenic]

The HTML spec already allows this. The trick is that the src setter, like all setters on HTML elements, does a conversion (in this case the conversion is named "USVString", which means ToString plus censoring surrogate pairs). Since URL defines a toString() method, it all works as you'd hope.

I'll close this since the HTML spec is fine as-is, but feel free to ask more questions in the closed thread!

[TimvdLippe]

Thanks @domenic for the speedy reply and explaining the intent of USVString (TIL)! I filed microsoft/TypeScript#43066 based on that.