Why without () this theres a delay,but with () function is called instantly without delaying for 3secnds..

Question

function onTimeout()
{
alert("hey maaa");

}
var timer=setTimeout(onTimeout(),3000);

Answer 1

because with () you call the function instantly instead of setting a timeout for it

without () you are passing the function to the setTimeout function which creates a timer for a given function

that where the difference lies:
passing a function is done without ()
calling a function is done with ()