block-parse.jsx

const { parse, registerBlock } = wp.blocks;
const { attr, html } = parse;

registerBlock( 'wp/image', {
	schema: {
		src: attr( 'img', 'src' ),
		alt: attr( 'img', 'alt' ),
		caption: html( 'figcaption' )
	},

	edit( { attributes, setAttributes } ) {
		const { src, alt, caption } = attributes;

		return (
			<figure>
				<EditableImage
					src={ src }
					alt={ alt }
					onChange={ ( attrs ) => setAttributes( attrs ) } />
				<EditableText
					value={ caption }
					onChange={ ( value ) => setAttributes( { caption: value } ) } />
			</figure>
		);
	},

	save( { attributes } ) {
		const { src, alt, caption } = attributes;

		return (
			<figure>
				<img src={ src } alt={ alt } />
				{ caption ? <figcaption>{ caption }</figcaption> : null }
			</figure>
		);
	}
} );