discourse/discourse · error · Error

${this.constructor.name} must implement evaluate()

Error message

${this.constructor.name} must implement evaluate()

What it means

Error "${this.constructor.name} must implement evaluate()" thrown in discourse/discourse.

Source

Thrown at frontend/discourse/app/blocks/conditions/condition.ts:266

      ? this.resolveSource(args, context)
      : this.defaultSource;
  }

  /**
   * Evaluates whether the condition passes.
   * Called at render time to determine if a block should be shown.
   *
   * **Note: This method MUST be pure and idempotent.** It may be called
   * multiple times during a single render cycle (e.g., when debug logging
   * is enabled), and should not have side effects.
   *
   * @param args - The condition arguments from the layout entry.
   * @param context - Evaluation context from the blocks service.
   * @returns True if condition passes, false otherwise.
   */
  // eslint-disable-next-line @typescript-eslint/no-unused-vars
  evaluate(args: Record<string, unknown>, context?: ConditionContext): boolean {
    throw new Error(`${this.constructor.name} must implement evaluate()`);
  }

  /**
   * Returns the resolved value for debug logging purposes.
   *
   * Override this method in subclasses to provide custom resolved values
   * for conditions that don't use the standard `source` parameter.
   * For example, the `outletArg` condition uses a `path` parameter
   * to resolve values from outlet args.
   *
   * @param args - The condition arguments from the layout entry.
   * @param context - Evaluation context containing outletArgs.
   * @returns Object with resolved value, or undefined if this condition doesn't resolve values.
   */
  getResolvedValueForLogging(
    args: Record<string, unknown>,
    context?: ConditionContext
  ): ConditionResolvedValue | undefined {

View on GitHub (pinned to 1b2d7253e8)

When it happens

Trigger: Thrown at frontend/discourse/app/blocks/conditions/condition.ts:266 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/10759527e7ca96c6. Report an issue: GitHub.