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

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
function makeOne() { class C { args = { ...arguments }; // SyntaxError: arguments is not valid in fields } return new C(); }
js
let CArgs; class C { static { CArgs = arguments; // SyntaxError: arguments is not valid in fields } }
js
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
function makeOne() { const _arguments = arguments; class C { args = { ..._arguments }; // Only the identifier is forbidden } return new C(); }

See also