On: Faster JavaScript Calls

[colejohnson66]

But in Java (and similar), you have to be explicit about varargs. In JavaScript, every function supports varargs. This will run just fine:

    function print(arg) {
        console.log(arg);
    }
    print("a", "b", "c");

It’ll only output "a", obviously. In fact, this will run just fine too:

    print();

You’ll get "undefined" in the console, but it’ll work.

JavaScript’s nature is that arguments are in the "arguments" pseudo-array, and the parameters are just fancy names for different values in "arguments". See:

    function count() {
        console.log(arguments.length);
    }
    count();
    count("a");
    count("a", "b");

In order, you’ll get: 0, 1, and 2. Despite the fact that "count" has no parameters in the definition.

In the first function ("print"), "arg" is just syntax sugar for "arguments[0]".

What I’m getting at is: in C, Java, etc., the compiler knows what is a varargs function and what isn’t. In JavaScript, the interpreter/compiler doesn’t and has to assume everything is.

[masklinn → colejohnson66]

> In the first function ("print"), "arg" is just syntax sugar for "arguments[0]".

So much so that they reflect one another: you can set `arguments[0]` and retrieve that value from `arg`, and the other way around:

    function foo(arg0, arg1) {
      arg0 = "foo";
      arguments[1] = "bar";
      console.log(Array.from(arguments), arg0, arg1);
    }
    foo(1, 2)

will log

    [ "foo", "bar" ] foo bar

Although in reality optimising engines treat `arguments` as a keyword of sorts: they will not reify the object if they don't have to. However this meant they had to deoptimise a fair bit before the "spread" arguments arrived as that was how you'd call your "super".

[desert_boi → colejohnson66]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

[colejohnson66 → desert_boi]

Hence, “pseudo-array”

[The_rationalist → colejohnson66]

Great explanation and I think you are right for Java, Kotlin, etc. But what about dynamic languages on the JVM such as GraalJS, groovy, etc?