emberjs/ember.js · error · Error

Custom modifier managers must have a `capabilities` property

Error message

Custom modifier managers must have a `capabilities` property that is the result of calling the `capabilities('3.22')` (imported via `import { capabilities } from '@ember/modifier';`). Received: `${JSON.stringify(delegate.capabilities)}` for: `${delegate}`

What it means

Error "Custom modifier managers must have a `capabilities` property that is the result of calling the `capabilities('3.22')` (imported via `import { capabilities } from '@ember/modifier';`). Received: `${JSON.stringify(delegate.capabilities)}` for: `${delegate}`" thrown in emberjs/ember.js.

Source

Thrown at packages/@glimmer/manager/lib/public/modifier.ts:93

  O extends Owner,
  ModifierInstance,
> implements InternalModifierManager<CustomModifierState<ModifierInstance>> {
  private componentManagerDelegates = new WeakMap<O, ModifierManager<ModifierInstance>>();

  constructor(private factory: ManagerFactory<O, ModifierManager<ModifierInstance>>) {}

  private getDelegateFor(owner: O) {
    let { componentManagerDelegates } = this;
    let delegate = componentManagerDelegates.get(owner);

    if (delegate === undefined) {
      let { factory } = this;
      delegate = factory(owner);

      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion -- @fixme
      if (DEBUG && !FROM_CAPABILITIES!.has(delegate.capabilities)) {
        // TODO: This error message should make sense in both Ember and Glimmer https://github.com/glimmerjs/glimmer-vm/issues/1200
        throw new Error(
          `Custom modifier managers must have a \`capabilities\` property that is the result of calling the \`capabilities('3.22')\` (imported via \`import { capabilities } from '@ember/modifier';\`). Received: \`${JSON.stringify(
            delegate.capabilities
            // eslint-disable-next-line @typescript-eslint/no-base-to-string
          )}\` for: \`${delegate}\``
        );
      }

      componentManagerDelegates.set(owner, delegate);
    }

    return delegate;
  }

  create(owner: O, element: SimpleElement, definition: object, capturedArgs: CapturedArguments) {
    let delegate = this.getDelegateFor(owner);

    let args = argsProxyFor(capturedArgs, 'modifier');
    let instance: ModifierInstance = delegate.createModifier(definition, args);

View on GitHub (pinned to 26f97246a8)

When it happens

Trigger: Thrown at packages/@glimmer/manager/lib/public/modifier.ts:93 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/dd1eee8bdd4140fb. Report an issue: GitHub.