How to use the @ckeditor/ckeditor5-ui/src/model function in @ckeditor/ckeditor5-ui

function _prepareListOptions( options, command ) {
	const itemDefinitions = new Collection();

	// Create dropdown items.
	for ( const option of options ) {
		const def = {
			type: 'button',
			model: new Model( {
				commandName: FONT_FAMILY,
				commandParam: option.model,
				label: option.title,
				withText: true
			} )
		};

		def.model.bind( 'isOn' ).to( command, 'value', value => value === option.model );

		// Try to set a dropdown list item style.
		if ( option.view && option.view.styles ) {
			def.model.set( 'labelStyle', `font-family: ${ option.view.styles[ 'font-family' ] }` );
		}

		itemDefinitions.add( def );
	}

function addListOption( option, editor, commands, itemDefinitions ) {
	const model = option.model = new Model( option.model );
	const { commandName, bindIsOn } = option.model;

	if ( option.type !== 'separator' ) {
		const command = editor.commands.get( commandName );

		commands.push( command );

		model.set( { commandName } );

		model.bind( 'isEnabled' ).to( command );

		if ( bindIsOn ) {
			model.bind( 'isOn' ).to( command, 'value' );
		}
	}

function _prepareListOptions( options, command ) {
	const itemDefinitions = new Collection();

	for ( const option of options ) {
		const def = {
			type: 'button',
			model: new Model( {
				commandName: FONT_SIZE,
				commandParam: option.model,
				label: option.title,
				class: 'ck-fontsize-option',
				withText: true
			} )
		};

		if ( option.view && option.view.styles ) {
			def.model.set( 'labelStyle', `font-size:${ option.view.styles[ 'font-size' ] }` );
		}

		if ( option.view && option.view.classes ) {
			def.model.set( 'class', `${ def.model.class } ${ option.view.classes }` );
		}