up.form up.validate(element, [options])

JavaScript function

Render a new form state from its current field values, to show validation errors or update dependent fields.

Typical use cases are to show validation errors after a field was changed or to update forms where one field depends on the value of another.

up.validate() submits the given element's form with an additional X-Up-Validate HTTP header. Upon seeing this header, the server is expected to validate (but not commit) the form submission and render a new form state. See this example for control flow on the server.

To automatically update a form after a field was changed, use the the [up-validate] attribute. You may combine [up-validate] and up.validate() within the same form. Their updates will be batched together to prevent race conditions.

Controlling what is updated

up.validate() always submits the entire form with its current field values to the form's [action] path. Typically only a fragment of the form is updated with the response. This minimizes the chance for loss of transient state like scroll positions, cursor selection or user input while the request is in flight.

Passing a form field will update the closest form group around the field:

up.validate('input[name=email]')

If the given field has an [up-validate] attribute with a custom target selector, that selector will be updated instead.

You may also update arbitrary elements within the form:

up.validate('.preview')

You may also choose to re-render an entire form. In this case it is recommended to disable fields while rendering. This prevents the loss of user input made while the request is in flight:

up.validate('form', { disable: true })

Multiple validations are batched together

In order to prevent race conditions, multiple calls of up.validate() within the same task are consolidated into a single request. For instance, the following will send a single request targeting .foo, .bar:

up.validate('.foo')
up.validate('.bar')

Validating the same target multiple times will also only send a single request. For instance, the following will send a single request targeting .qux:

up.validate('.qux')
up.validate('.qux')

When one of your target elements is an ancestor of another target, Unpoly will only request the ancestor. For instance, the following would send a single request targeting form:

up.validate('input[name=email]')
up.validate('form')

Also see preventing race conditions.