Code node doesnt support custom method?

Questions
1

here’s my code:

Array.prototype.shuffle = function() {
  const shuffled = [...this]; // Create a copy to avoid mutating original
  for (let i = shuffled.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [shuffled[i], shuffled[j]] = [shuffled[j], shuffled[i]];
  }
  return shuffled;
};

and it gives error:
prototype 'shuffle' does not exist on type 'any[]'

2

Avoid extending prototypes. Instead of using Array.prototype.shuffle, define a regular function:

function shuffle(arr) {
const shuffled = [...arr];
for (let i = shuffled.length - 1; i > 0; i--) {
const j = Math.floor(Math.random() * (i + 1));
[shuffled[i], shuffled[j]] = [shuffled[j], shuffled[i]];
}
return shuffled;
}

// Usage:
const result = shuffle([1, 2, 3, 4]);

If you really need to extend the prototype, you can do it like this (safely):

interface Array<T> {
shuffle(): T[];
}

Array.prototype.shuffle = function() {
const shuffled = [...this];
for (let i = shuffled.length - 1; i > 0; i--) {
const j = Math.floor(Math.random() * (i + 1));
[shuffled[i], shuffled[j]] = [shuffled[j], shuffled[i]];
}
return shuffled;
};

const myArray = [1, 2, 3];
const shuffled = myArray.shuffle();

But this may still cause warnings depending on the Code Node sandbox in n8n, and is not the recommended option.