function duke_blocks() {

    wp_register_script(
        'wb-blocks-js',
        get_template_directory_uri() . '/inc/meta-block.js',
        array( 'wp-blocks', 'wp-editor', 'wp-element','wp-components' )
    );
    register_block_type( 'dukeyin/audio-url', array(
        'editor_script' => 'wb-blocks-js',
    ) );

}
add_action( 'init', 'duke_blocks' );

function duke_register_block_meta() {

    register_meta( 'post', 'audio-url', array(
        'show_in_rest' => true,
        'single' => true,
        'type' => 'string',
        'object_subtype' => 'audio',
    ) );

}

add_action( 'init', 'duke_register_block_meta' );

( function( wp ) {
    var el = wp.element.createElement;
    var registerBlockType = wp.blocks.registerBlockType;
    var TextControl = wp.components.TextControl;

    registerBlockType( 'dukeyin/audio-url', {
    title: 'Audio file URL',
    icon: 'media-audio',
    category: 'layout',
    attributes: {
        blockValue: {
            type: 'string',
            source: 'meta',
            meta: 'audio-url',
        }
    },

    edit: function( props ) {
        var setAttributes = props.setAttributes;

        function updateBlockValue( blockValue ) {
            setAttributes({ blockValue });
        }

        return el(
           'div',
           { className: "audio-url" },
            el( 'h5',{}, 'URL to audio file:'),
            el (TextControl,
            {
                onChange: updateBlockValue,
                value: props.attributes. blockValue,
            })
        );
    },

    save: function( props ) {
         return null;
    },
    } );
} )( window.wp );