¿Cómo interceptar decimales usando js?

parseFloat(${aaa}). toFixed(2);?

//Por ejemplo

parseFloat("12.777777777 "). toFixed(2);

//12.78

/*Sin redondeo*/

(${aaa}). match(new?RegExp("\\d+\\.\\d{ "?+?2?+?"}", "gm"))? ;

//Por ejemplo

("12.777777777777777").Match(new?RegExp("\\d+\\.\\d{ "?+?2?+? " }", "GM"));

//12.77