Question

I know arguments.length method , but this returns the number of arguments the function was called with.

What I need instead is the number of arguments that function requires, so for example

function myFunc(arg1,arg2,arg3) {
  alert("number of passed args:" + arguments.length);
  alert("number of required args:" + /*the code I'm asking for*/);
};

myFunc('some arg');

So myFunc() would return two alerts saying 1 and 3.

Any way to do that ?

Answer 1

Another, he deprecated arguments.caller.length property holds this value.

function myFunc(arg1,arg2,arg3) {
    alert("number of passed args:" + arguments.length);
    alert("number of required args:" + arguments.caller.length);
}

Another method to get the number of formal parameters is by using the length property of the function. The function’s name has to be known for this method:

function myFunc(arg1,arg2,arg3) {
    alert("number of passed args:" + arguments.length);
    alert("number of required args:" + myFunc.length);
}