app.js

function getProducts(categoryId){
   let results;
    connection.query('SELECT * FROM products WHERE category = ?', [categoryId],
        function (error, products, fields) {
            if (error) throw error;
            
            for(let i = 0; i < products.length; i++){
                connection.query('SELECT image FROM productimages WHERE productID = ?', [products[i].productID], 
                    function (error2, images, fields2){
                        if (error2) throw error2;
                        products[i].images = images;
                });
                connection.query('SELECT * FROM optionsofproduct as op, productoptions as po WHERE op.productID = ? AND op.optionID = po.optionID', [products[i].productID], 
                    function (error2, options, fields2){
                        if (error2) throw error2;
                        products[i].options = options;
                        
                });
            }
          results = products;
    });
    return results;
}