alfresco-content-app/docs/extending/creating-custom-evaluators.md

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Creating custom evaluators

Creating custom evaluators

Rule evaluators are plain JavaScript (or TypeScript) functions that take RuleContext references and an optional list of RuleParameter instances.

Application provides a special RuleEvaluator type alias for evaluator functions:

export type RuleEvaluator = (context: RuleContext, ...args: any[]) => boolean;

Create a function that is going to check if a user has selected one or multiple nodes.

export function hasSelection(
  context: RuleContext,
  ...args: RuleParameter[]
): boolean {
  return !context.selection.isEmpty;
}

The context is a reference to a special instance of the RuleContext type, that provides each evaluator access to runtime entities.

export interface RuleContext {
  selection: SelectionState;
  navigation: NavigationState;
  permissions: NodePermissions;

  getEvaluator(key: string): RuleEvaluator;
}

The SelectionState interface exposes information about the global selection state:

export interface SelectionState {
  count: number;
  nodes: MinimalNodeEntity[];
  libraries: SiteEntry[];
  isEmpty: boolean;
  first?: MinimalNodeEntity;
  last?: MinimalNodeEntity;
  folder?: MinimalNodeEntity;
  file?: MinimalNodeEntity;
  library?: SiteEntry;
}

Next, register the function you have created earlier with the ExtensionService and give it a unique identifier:

extensions.setEvaluators({
  'plugin1.rules.hasSelection': hasSelection
});

Now, the plugin1.rules.hasSelection evaluator can be used as an inline rule reference, or part of the composite rule like core.every.

Tip: See the Registration section for more details on how to register your own entries to be re-used at runtime.