Parameter Validation

One of the advantages of auto-generating our action creators is that we can automatically provide some limited validation.

By default all action creator invocations will insure the correct number of parameters are provided. As an example, if you invoke the actions.userMsg(msg) without the msg parameter, the following exception will be thrown:

  ERROR: Action Creator userMsg(msg) expecting 1 parameter, but received 0

You can provide app-specific parameter validation by using the actionMeta.ratify property. This is an app-supplied function (ratifyFn()) that accepts the same set of parameters defined in actionMeta.traits, and performs validation via an app-specific means (typically thrown exceptions), returning an array of the arguments passed in.

As an example, to insure only strings are passed into actions.userMsg(msg), do the following:

import {generateActions} from 'action-u';

const actions = generateActions({
  userMsg: {
              actionMeta: {
                traits: ['msg'],
                ratify(msg) { // NEW
                  assert(isString(msg), `ERROR: userMsg(msg) the supplied msg is NOT a string: ${msg}`);
                  return [msg];
    close: {
              actionMeta: {}

NOTE: The reason that ratifyFn() returns an array of the arguments passed in is to allow it to inject default semantics (see: Defaulting Parameters). You should never attempt to return the built-in arguments array-like object for two reasons:

  1. applied defaults are NOT reflected in arguments, and
  2. arguments are not bound to arrow functions.

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