discourse/discourse · error · Error

[FormKit]: the @data property expects a POJO.

Error message

[FormKit]: the @data property expects a POJO.

What it means

A type-coercion guard in the FormKit changeset constructor: the @data passed to the form is not a POJO, so Immer's `produce` rejected it (message containing "[Immer]") and the original cause is rethrown wrapped. The faulty input is the non-plain-object value bound to `<form.Form @data>` (e.g. an Ember object, class instance, or undefined-derived value).

Solutions

1. Pass a plain JavaScript object as @data, e.g. `{ ...model }` instead of the model instance
2. Convert arrays/Map/Set or Ember proxies to POJOs before handing them to the form
3. Inspect `e.cause` for the underlying Immer error if the data looks like a POJO

When it happens

Trigger: Thrown at frontend/discourse/app/form-kit/lib/fk-form-data.js:51 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of discourse/discourse@1b2d7253e8 (2026-08-26). Data as JSON: /api/errors/795367a60348a031. Report an issue: GitHub.

Appendix: source

Thrown at frontend/discourse/app/form-kit/lib/fk-form-data.js:51

  @tracked patches = [];

  /**
   * The inverse patches to be applied, useful for rollback.
   * @type {Array}
   */
  @tracked inversePatches = [];

  /**
   * Creates an instance of Changeset.
   * @param {any} data - The initial data.
   */
  constructor(data) {
    try {
      this.data = produce(data, () => {});
      this.draftData = produce(data, () => {});
    } catch (e) {
      if (e.message.includes("[Immer]")) {
        throw new Error("[FormKit]: the @data property expects a POJO.", {
          cause: e,
        });
      }
    }
  }

  /**
   * Checks if the changeset is valid.
   * @return {boolean} True if there are no errors.
   */
  get isValid() {
    return Object.keys(this.errors).length === 0;
  }

  /**
   * Checks if the changeset is invalid.
   * @return {boolean} True if there are errors.
   */

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