open-consul/ui/packages/consul-ui/app/modifiers/validate.mdx

# validate

Simple validation modifier to make it super easy to add validations to your
form elements.

**Please note:** You probably should be using one of our many (soon) Form
Components like `<TextInput />` instead of using this. If you have something
more custom that needs validation support, then read on!

The `validate` modifier primarily requires a `validations` argument passing to
it. The shape of this is an object containing property/validation pairs.
Generally you will only need to pass one of these, and in this case the
property is also used for naming any resulting errors. For example `Name` will
result in `{Name: 'Name error message'}` being thrown/called/passed to the
state's context or the `onchange` event.

In the future we are looking to support validation based on other properties
in the passed `item` positional argument, hence the slightly more complicated
shape of this `validations` argument.

Validation objects currently contain 2 properties: `test` and `error`. `test`
is used to provide a Regular Expression used to validate the users' input, and
the `error` property is a humanized string which is provided to the state's
context/onchange event. We may add support for a `success` message in the
future for when the validation is in a successful state.

Please note: you should only need to use either the `chart` argument or the
`onchange` listener, not both.


```hbs preview-template

{{#let

  (hash
    help='Must be a valid DNS hostname. Must contain 1-64 characters (numbers, letters, and hyphens), and must begin with a letter. Once created, this cannot be changed.'
    Name=(array
      (hash
        test='^[a-zA-Z0-9]([a-zA-Z0-9-]{0,62}[a-zA-Z0-9])?$'
        error='Name must be a valid DNS hostname.'
      )
    )
  )

as |validations|}}

<figure>
  <figcaption>Valid to begin with</figcaption>
  <input
    {{validate
      validations=validations
      onchange=(fn (mut this.validErrors))
    }}
    type="text"
    value={{'this-is-valid-text-add-a-space-to-see-the-validation-error'}}
  />
  {{#if this.validErrors.Name}}
    <br /><strong>{{this.validErrors.Name.message}}</strong>
  {{/if}}
</figure>

<figure>
  <figcaption>Invalid to begin with</figcaption>
  <input
    {{validate
      validations=validations
      onchange=(fn (mut this.invalidErrors))
    }}
    type="text"
    value={{"not-valid-text remove-the-space"}}
  />
  {{#if this.invalidErrors.Name}}
    <br /><strong>{{this.invalidErrors.Name.message}}</strong>
  {{/if}}
</figure>

{{/let}}
```

## Positional Arguments

| Argument | Type | Default | Description |
| --- | --- | --- | --- |
| `item` | `object` |  | An object containing properties to be validated |


## Named Arguments

| Argument | Type | Default | Description |
| --- | --- | --- | --- |
| `validations` | `object` |  | Validation shaped object to use for the validation |
| `onchange` | `object` |  |  A function called when the validations state changes form successful to erroneous and vice versa |
| `chart` | `object` |  | A statechart object following a state/dispatch interface to use as an alternative t onchange |