SyntaxError: arguments is not valid in fields

Message

SyntaxError: 'arguments' is not allowed in class field initializer or static initialization block (V8-based)
SyntaxError: arguments is not valid in fields (Firefox)
SyntaxError: Unexpected identifier 'arguments'. Cannot reference 'arguments' in class field initializer. (Safari)

Error type

What went wrong?

A class field initializer expression or a class static initialization block does not have arguments in its scope. Trying to access it is a syntax error.

• This is true even if arguments is bound in a parent scope (such as when the class is nested in a non-arrow function).
• A non-arrow function declared within this scope will still bind its own arguments and read it normally.

Examples

function makeOne() {
  class C {
    args = { ...arguments }; // SyntaxError: arguments is not valid in fields
  }
  return new C();
}

let CArgs;
class C {
  static {
    CArgs = arguments; // SyntaxError: arguments is not valid in fields
  }
}

class C {
  args = {};
  constructor() {
    this.args = arguments; // You can use arguments in constructors
  }
  myMethod() {
    this.args = arguments; // You can also use it in methods
  }
}

function makeOne() {
  const _arguments = arguments;
  class C {
    args = { ..._arguments }; // Only the identifier is forbidden
  }
  return new C();
}

See also

• Classes
• Public class fields
• Static initialization blocks