Is there a way to change a function's arguments from another javascript function?

Question

I'm trying to change function arguments inside another function and then returns it to callee function. I'm trying something like this:

function func(a,b,c) {
    console.log(arguments, a, b, c); //[1, true, "a"] 1 true "a"
  arguments[0] = 2;
    console.log(arguments, a, b, c); //[2, true, "a"] 2 true "a"
  arguments = ArgumentsToNumber.apply(this, arguments);
  console.log(arguments, a, b, c); //[2, 1, NaN] 2 true "a"
}

function ArgumentsToNumber() {
    for (let i = 0; i < arguments.length; i++) {
    arguments[i] = Number(arguments[i]);
  }
  return arguments;
}

func(1, true, 'a');

I want changes in a, b and c variables.

Why not just use array.map in func? arguments = arguments.map((argument) => Number(argument)) — Akshat Mahajan
– Akshat Mahajan, Commented Apr 3, 2016 at 18:26
@AkshatMahajan That will thrown an error. arguments is not an array — Rajaprabhu Aravindasamy
– Rajaprabhu Aravindasamy, Commented Apr 3, 2016 at 18:27
This doesn't look like good practice arguments[0] = 2. You probably want to convert the arguments to an array first. [].slice.call(arguments) or map over them in some way like [].map.call(arguments, callback) — elclanrs
– elclanrs, Commented Apr 3, 2016 at 18:27
You must borrow map from array e.g. [].map.call(arguments, Number) — csharpfolk
– csharpfolk, Commented Apr 3, 2016 at 18:27

Oriol · Accepted Answer · 2016-04-03 18:34:17Z

1

You must pass the Arguments object itself, instead of using it as an array-like in apply:

function func(a, b, c) {
  console.log(a, b, c); // 1, true, "a"
  arguments[0] = 2;
  console.log(a, b, c); // 2, true, "a"
  argumentsToNumber(arguments);
  console.log(a, b, c); // 2,    1, NaN
}
function argumentsToNumber(args) {
  for (let i = 0; i < args.length; i++)
    args[i] = +args[i];
}
func(1, true, 'a');

Note that changing the arguments in another function has bad performance.

answered Apr 3, 2016 at 18:34

Oriol

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2 Comments

Oriol Over a year ago

@HenriCavalcante See for example jspatterns.com/arguments-considered-harmful

dandavis Over a year ago

it's arguments.callee or passing the whole arguments object that slows things down, but even those don't slow down code very much. 3site.eu/jstests/arguments.callee.calls.html?times=50000

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