Don't Update Function Argument Values

Do not change those non-primitive function arguments without understanding the significant implications of your action.

Programming languages have pass by reference and pass by value to pass arguments to a function. Javascript passes values for primitives, but references when you are trying to pass objects.

Changing arguments within a function will change the arguments for ever.

function hello(addressee) {
  addressee.name = "Mr. Anderson";
  return "Hello " + addressee.name;
}

const person = { name: "world" };
console.log(hello(person));
// Hello Mr. Anderson

console.log("person: ", person);
// person:  { name: 'Mr. Anderson' }

It is a disaster if the world is treated as Mr. Anderson.

The simplest way to avoid this is by localizing the object in the function. You can do this with a spread operator or a rest operator.

function hello({ ...addressee }) {
  addressee.name = "Mr. Anderson";
  return "Hello " + addressee.name;
}

const person = { name: "world" };
console.log(hello(person));
// Hello Mr. Anderson

console.log("person: ", person);
person: {
  name: "world";
}

In the above code we copy the original object and make any changes locally within the function. The changes do not impact the object passed as argument.