Validators

Overview

If a bound predicate is a way to check a single predicate against some fields, then a validator is a way to check many bound predicates against a model.

Note

Internally validators keep track of pending predicate results and a cache of results for the previous inputs, which means they need an extra layer of indirection if they are to be used with multiple models.

Creating a validator

Since validators are simply a list of bound predicates, creating one is a short two-step process:

1. Create a validators definition that can be reused:

   import * as P from "manner/predicates";
   import * as V from "manner/validators";
   let someValidators = V.validators(
     P.is('one', P.equalTo(42)),
     P.is('two', P.notNull()));
   

2. Instantiate a validators definition to create an instance, a validator, with its own state suitable for repeated use with one particular model:

   let formValidator = V.instantiate(someValidators);
   formValidator(my_model);  // => Validation results
   

The ultimate result of invoking an validator is an Immutable.Map of field names to predicate status, which can then be used to update the state of a form, perhaps indicating which fields failed to validate.

Long-running predicates

A validator takes an optional second argument: a callback function, passed the result of a bound predicate, that is called as soon as the result is resolved.

Asynchronous predicates may prevent a validator from resolving for an extended period of time thus delaying any important user interface updates, in this case the callback function can be used to update the user interface as predicate results are resolved.