Currently, there is no JavaScript syntax for using Agents. To use Agents from JavaScript SDK, refer to the Agents documentation in SQL and execute SQL queries as below. 
const query = `
    CREATE AGENT my_agent
    USING
        model = {
            "provider": "openai",
            "model_name" : "gpt-4o",
            "api_key": "sk-abc123"
        },
        data = {
            "knowledge_bases": ["mindsdb.sales_kb", "mindsdb.orders_kb"],
            "tables": ["postgres_conn.customers", "mysql_conn.products"]
        },
        prompt_template='
            mindsdb.sales_kb stores sales analytics data
            mindsdb.orders_kb stores order data
            postgres_conn.customers stores customers data
            mysql_conn.products stores products data
        ';
    `;
const queryResult = await MindsDB.SQL.runQuery(query);