Question

I need to pass arguments onto a callback function as real arguments. How do I do that? callback requires a variable number of arguments.

Example function like this:

var func = function (callback) {
  doSomething(function () {
    // the goal is to pass on the arguments object to the callback function as real arguments
    callback(arguments)
  });
}

Thanks in advance.

It might be a similar question to this:
Is it possible to send a variable number of arguments to a JavaScript function?

But I didn’t understand that question nor the answers.

Edit: If possible, I would like to not pollute global.

Answer 1

Use apply to invoke the callback so the array items gets passed as individual arguments to the function.

callback.apply(this, arguments);

apply takes the context, and an array as an argument, and each item of the array can be passed as a named argument of the function being invoked.

function two(first, second) {
    alert(first), alert(second);
}

two.apply(null, ["Hello", "World"]); // alerts "Hello", then "World"

Implementations of ES3 required that the second argument to apply be either an array, or an arguments object. ES5 makes it more liberal in that as long as it resembles an array – has a length property, and corresponding integer indexes, it will work.