SyntaxError: arguments is not valid in fields

The JavaScript exception "SyntaxError: arguments is not valid in fields" occurs when the arguments identifier is read in a class field initializer or in a static initialization block, outside of a non-arrow function.

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#

{{jsxref("SyntaxError")}}

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#

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

```js example-bad
let CArgs;
class C {
  static {
    CArgs = arguments; // SyntaxError: arguments is not valid in fields
  }
}

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

```js example-good
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