Javascript中是否为匿名调用的函数提供了参数计数？

Question

(function (a, b, c) {

  console.log(arguments.length); // 2

} (1, 2) )

When the above function runs, the function can tell it was called with only two arguments via the arguments object's length property.

Is there also a way for the function to tell that it was expecting 3 arguments since a, b, & c are listed in the definition of the function?

In the above function:

console.log( what?) === 3?

I read through this answer Get a function's arity but it requires a reference (such as a name) to the function and does not answer my question with respect to the console.log being inside the function.

Answer 1

Yes. Example:

function main(a, b, c) {
    console.log(main.length);
}

main(1, 2);    

See this Fiddle

Answer 2

You can name your function expression ^[1] and use that reference to get the arity of the function via its .length property :

(function iefe(a, b, c) {
    console.log(arguments.length); // 2
    console.log(iefe.length); // 3
}(1, 2));

_{1: If you don't care about oldIE bugs. If you do and work in sloppy mode, arguments.callee might be a better option. Of course you can also use an identifier-leaking function declaration or variable assignment, or - as you always refer to the same function anyway - use a constant value.}