if

$if

This is a conditional operator that evaluates a predicate for truthiness.

If the predicate returns a truthy value, $if will invoke any provided success action with the original input. If not provided, the default success action will simply return the original input.

If the predicate returns a falsey value or rejects/throws, $if will return the result of invoking the failure action on the original input. The default failure action will return undefined.

This processor can act as a constraint if the success or failure actions throw when triggered.

To pass the predicate results to the actions instead of the input, see $check. To test for success rather than truthiness, see $gate.

Parameters

• predicate (processor, optional): Evaluated for truthiness. If omitted, the input itself is used as the predicate.
• success (processor, optional): Invoked with the original input on truthy predicate result. Default: returns input as-is.
• failure (processor, optional): Invoked with the original input on falsey predicate result or throw. Default: returns undefined.

Array form: {$if: [predicate, success, failure]} Object form: {$if: {predicate: ..., success: ..., failure: ...}} Aliases: predicate may also be written as condition or cond.

Example

// Normalize an optional port — keep it if numeric, otherwise drop it
new Schema('object', {
  port: new Schema('number').normalizer({
    $if: ['$numeric', '$number', null]
  }),
})

// Conditionally require an API key when a flag is set
new Schema('object', {
  useApiKey: new Schema('boolean'),
  apiKey: new Schema('string').validator({
    $if: [
      {$reference: 'useApiKey'},
      '$non-empty',
    ]
  }),
})