Can't run function on variable-length argument array in JavaScript

Question

I am trying to perform a function on my arguments, which is variable length. I can't seem to run any function on my arguments array, including sort.

function findKeyFromNotes()
    {
         var notes = arguments.slice(); 
         return notes;  
    }

I am getting this error:

TypeError: arguments.slice is not a function

Thanks, Nakul

@ScottHunter it doesn't matter, the arguments object doesn't have a .slice() method. — Pointy
– Pointy, Commented Nov 5, 2019 at 0:29
@StackSlave that's a very common pattern, but it's not the best idea because leaking the arguments object makes it basically impossible to optimize the function (because arguments does weird things). — Pointy
– Pointy, Commented Nov 5, 2019 at 0:57

Pointy · Accepted Answer · 2019-11-05 00:31:49Z

1

In modern JavaScript, you can use the spread syntax to collect all arguments into a single array value:

function findKeyFromNotes(... notes) {
  // notes will be an array
}

In "traditional" JavaScript the best thing to do would be:

function findKeyFromNotes() {
  var notes = [];
  for (var i = 0; i < arguments.length; ++i) notes[i] = arguments[i];
  // now notes is a plain array
}

answered Nov 5, 2019 at 0:31

Pointy

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2 Comments

Pointy Over a year ago

The common use of .slice() to convert arguments to an array is kind-of a bad idea because it seriously impedes JIT optimization.

Pointy Over a year ago

My comment does not apply to "strict" mode code however.

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