parse.js

const parse, { query, text, attr } = wp.blocks.parse;

const quote = parse( '<blockquote><p>...</p><p>...</p><cite>Andrew</cite></blockquote>', {
	text: query( 'p', text() ),
	cite: text( 'cite' )
} );

// { text: [ "...", "..." ], cite: "Andrew" }

const image = parse( '<figure><img src="img.png" alt="Image"><figcaption>An Image</figcaption></figure>', {
	src: attr( 'img', 'src' ),
	alt: attr( 'img', 'alt' ),
	caption: text( 'figcaption' )
} );

// { src: "img.png", alt: "Image", caption: "An Image" }