Attribute parsing should return true when attribute is set without value

[danielbachhuber]

Given an HTML element:

<audio src="#" loop>

When I parse the loop attribute on the element, the value should be true:

it( 'should return true if the attribute is set without value', () => {
	const result = parse( element, attr( 'audio', 'loop' ) );

	expect( result ).to.be.true;
} );

parse() currently returns undefined.

From WordPress/gutenberg#7322 (comment)

[danielbachhuber]

Debugging this further, prop( selector, 'attributes' )( node ) is returning undefined for <audio loop>

[aduth]

As low-level as hpq is meant to be, I don't know that true should necessarily be the expected return value, as this requires some understanding of boolean attributes, which I'm not strictly opposed to, but adds some complexity/maintenance burden to the library. That said, undefined is not expected. I would expect, based on hpq's reliance on one or other of Element#attributes or Element#getAttribute, that it should at least be the empty string.

var wrapper = document.createElement( 'div' );
wrapper.innerHTML = '<audio loop>';
var audio = wrapper.querySelector( 'audio' );
console.log( audio.getAttribute( 'loop' ) );
// ""
console.log( audio.attributes.loop.value );
// ""

[danielbachhuber]

Huh. Anyways, I got stuck on trying to figure out why prop( selector, 'attributes' )( node ) returned undefined, when I expected it to return an object.

[aduth]

It was a small mistake with the test changes in #4, where the element was not including the added markup since the additional markup was defined outside the root blockquote. With patch at #4 (comment), attr( 'audio', 'loop' ) returns the empty string as expected.