emberjs/ember.js · error · Error

Object.keys() was called on the positional arguments array f

Error message

Object.keys() was called on the positional arguments array for a ${type}, which is not supported. This function is a low-level function that should not need to be called for positional argument arrays. You may be attempting to iterate over the array using for...in instead of for...of.

What it means

Error "Object.keys() was called on the positional arguments array for a ${type}, which is not supported. This function is a low-level function that should not need to be called for positional argument arrays. You may be attempting to iterate over the array using for...in instead of for...of." thrown in emberjs/ember.js.

Source

Thrown at packages/@glimmer/manager/lib/util/args-proxy.ts:165

  const namedHandler = new NamedArgsProxy(named);
  const positionalHandler = new PositionalArgsProxy(positional);

  // eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
  const namedTarget = Object.create(null);
  const positionalTarget: unknown[] = [];

  if (DEBUG) {
    const setHandler = function (_target: unknown, prop: symbol | string | number): never {
      throw new Error(
        `You attempted to set ${String(
          prop
        )} on the arguments of a component, helper, or modifier. Arguments are immutable and cannot be updated directly; they always represent the values that are passed down. If you want to set default values, you should use a getter and local tracked state instead.`
      );
    };

    const forInDebugHandler = (): never => {
      throw new Error(
        `Object.keys() was called on the positional arguments array for a ${type}, which is not supported. This function is a low-level function that should not need to be called for positional argument arrays. You may be attempting to iterate over the array using for...in instead of for...of.`
      );
    };

    namedHandler.set = setHandler;
    positionalHandler.set = setHandler;
    positionalHandler.ownKeys = forInDebugHandler;
  }

  // eslint-disable-next-line @typescript-eslint/no-unsafe-assignment
  const namedProxy = new Proxy(namedTarget, namedHandler);
  const positionalProxy = new Proxy(positionalTarget, positionalHandler);

  // eslint-disable-next-line @typescript-eslint/no-unsafe-argument
  setCustomTagFor(namedProxy, getNamedTag);
  setCustomTagFor(positionalProxy, getPositionalTag);

  return {

View on GitHub (pinned to 26f97246a8)

When it happens

Trigger: Thrown at packages/@glimmer/manager/lib/util/args-proxy.ts:165 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of emberjs/ember.js@26f97246a8 (2026-09-01). Data as JSON: /api/errors/d27e42278bd34877. Report an issue: GitHub.