Property Creator

computed([selector], getterFn[, matcher])

  • selector - optional selector to scope the computed property to a nested element
  • getterFn - a function that is invoked when the property is accessed
  • matcher - optional matcher for automatically creating assertions for a property

The computed() helper can be used to create reusable computed property getters. In addition to making computed properties reusable, the getterFn is passed the element node of the scoped element, or the interactor's own element when no selector is provided. If the getterFn function requires the element argument, an error will be thrown before the function is called if the element cannot be found. If no element argument is specified, this check is not performed.

If a matcher is supplied it is treated exactly like an assertion provided via the static assertions interactor property (see custom assertions). However, the first argument given to the matcher function is the result of the computed property.

import interactor, { computed } from 'interactor.js';

// custom property creator
function noValidate(selector) {
  return computed(
    // computed getter function
    element => element.noValidate,
    // computed assertion matcher
    noValidate => ({
      result: noValidate,
      message: () => `noValidate is ${noValidate}`

@interactor class FormInteractor {
  // reusable for other custom interactors
  noValidate = noValidate()

  // normal getters are fine
  get target() {
    return this.$().target;

  // shortcut for the element
  action = computed(element => {
    return element.action;