Description Allows you to create form and input tags.
Required Script <script async custom-element="amp-form" src="https://cdn.ampproject.org/v0/amp-form-0.1.js"></script>
Supported Layouts N/A
Examples See AMP By Example's amp-form examples.

Behavior

The amp-form extension allows you to create forms (<form>) to submit input fields in an AMP document. The amp-form extension also provides polyfills for some missing behaviors in browsers.

Before creating a <form>, you must include the required script for the <amp-form> extension, otherwise your document will be invalid. If you're using input tags for purposes other than submitting their values (e.g., inputs not inside a <form>), you do not need to load the amp-form extension.

Here's an example of a basic form:

Show full code

Attributes

target

Indicates where to display the form response after submitting the form. The value must be _blank or _top.

action

Specifies a server endpoint to handle the form input. The value must be an https URL (absolute or relative) and must not be a link to a CDN.

action-xhr

Specifies a server endpoint to handle the form input and submit the form via XMLHttpRequest (XHR). An XHR request (sometimes called an AJAX request) is where the browser would make the request without a full load of the page or opening a new page. Browsers will send the request in the background using the Fetch API when available and fallback to XMLHttpRequest API for older browsers.

This attribute is required for method=POST, and is optional for method=GET.

The value for action-xhr can be the same or a different endpoint than action and has the same action requirements above.

To learn about redirecting the user after successfully submitting the form, see the Redirecting after a submission section below.

other form attributes

All other form attributes are optional.

custom-validation-reporting

This is an optional attribute that enables and selects a custom validation reporting strategy. Valid values are one of: show-first-on-submit, show-all-on-submit or as-you-go.

See the Custom Validation section for more details.

Inputs and fields

Allowed:

  • Other form-related elements, including: <textarea>, <select>, <option>, <fieldset>, <label>, <input type=text>, <input type=submit>, and so on.
  • <input type=password> and <input type=file> inside of <form method=POST action-xhr>.
  • amp-selector

Not Allowed:

  • <input type=button>, <input type=image>
  • Most of the form-related attributes on inputs including: form, formaction, formtarget, formmethod and others.

(Relaxing some of these rules might be reconsidered in the future - please let us know if you require these and provide use cases).

For details on valid inputs and fields, see amp-form rules in the AMP validator specification.

Actions

The amp-form element exposes the following actions:

Action Description
submit Allows you to trigger the form submission on a specific action, for example, tapping a link, or submitting a form on input change.
clear Empties the values from each input in the form. This can allow users to quickly fill out forms a second time.

Events

The amp-form exposes the following events:

Event Fired when
submit The form is submitted and before the submission is complete.
submit-success The form submission is done and the response is a success.
submit-error The form submission is done and the response is an error.
verify Asynchronous verification is initiated.
verify-error Asynchronous verification is done and the response is an error.
valid The form's validation state changes to "valid" (in accordance with its reporting strategy).
invalid The form's validation state to "invalid" (in accordance with its reporting strategy).

These events can be used via the on attribute.

For example, the following listens to both the submit-success and submit-error events and shows different lightboxes depending on the event:

<form ... on="submit-success:success-lightbox;submit-error:error-lightbox" ...>
</form>

See the full example here.

Input events

AMP exposes change and input-debounced events on child <input> elements. This allows you to use the on attribute to execute an action on any element when an input value changes.

For example, a common use case is to submit a form on input change (selecting a radio button to answer a poll, choosing a language from a select input to translate a page, etc.).

Show full code

See the full example here.

Analytics triggers

The amp-form extension triggers the following events that you can track in your amp-analytics config:

Event Fired when
amp-form-submit A form request is initiated.
amp-form-submit-success A successful response is received (i.e, when the response has a status of 2XX).
amp-form-submit-error An unsuccessful response is received (i.e, when the response doesn't have a status of 2XX).

You can configure your analytics to send these events as in the following example:

<amp-analytics>
  <script type="application/json">
    {
      "requests": {
        "event": "https://www.example.com/analytics/event?eid=${eventId}",
        "searchEvent": "https://www.example.com/analytics/search?formId=${formId}&query=${formFields[query]}"
      },
      "triggers": {
        "formSubmit": {
          "on": "amp-form-submit",
          "request": "searchEvent"
        },
        "formSubmitSuccess": {
          "on": "amp-form-submit-success",
          "request": "event",
          "vars": {
            "eventId": "form-submit-success"
          }
        },
        "formSubmitError": {
          "on": "amp-form-submit-error",
          "request": "event",
          "vars": {
            "eventId": "form-submit-error"
          }
        }
      }
    }
  </script>
</amp-analytics>

All three events generate a set of variables that correspond to the specific form and the fields in the form. These variables can be used for analytics.

For example, the following form has one field:

<form action-xhr="/comment" method="POST" id="submit_form">
  <input type="text" name="comment" />
  <input type="submit" value="Comment" />
</form>

When the amp-form-submit, amp-form-submit-success, or amp-form-submit-error event fires, it generates the following variables containing the values that were specified in the form:

  • formId
  • formFields[comment]

Success/error response rendering

You can render success or error responses in your form by using extended templates, such as amp-mustache, or success responses through data binding with amp-bind and the following response attributes:

Response attribute Description
submit-success Can be used to display a success message if the response is successful (i.e., has a status of 2XX).
submit-error an be used to display a submission error if the response is unsuccessful (i.e., does not have a status of 2XX).
submitting Can be used to display a message when the form is submitting. The template for this attribute has access to the form's input fields for any display purposes. Please see the full form example below for how to use the submitting attribute.

To render responses with templating:

  • Apply a response attribute to any direct child of the <form> element.
  • Render the response in the child element by including a <template></template> tag inside it or by referencing a template with a template="id_of_other_template" attribute.
  • Provide a valid JSON object for responses to submit-success and submit-error. Both success and error responses should have a Content-Type: application/json header.

Example: Form displays success, error, and submitting messages

In the following example, the responses are rendered in an inline template inside the form.

<form ...>
  <fieldset>
    <input type="text" name="firstName" />
    ...
  </fieldset>
  <div verify-error>
    <template type="amp-mustache">
      There is a mistake in the form!
      {{#verifyErrors}}{{message}}{{/verifyErrors}}
    </template>
  </div>
  <div submitting>
    <template type="amp-mustache">
      Form submitting... Thank you for waiting {{name}}.
    </template>
  </div>
  <div submit-success>
    <template type="amp-mustache">
      Success! Thanks {{name}} for subscribing! Please make sure to check your email {{email}}
      to confirm! After that we'll start sending you weekly articles on {{#interests}}<b>{{name}}</b> {{/interests}}.
    </template>
  </div>
  <div submit-error>
    <template type="amp-mustache">
      Oops! {{name}}, {{message}}.
    </template>
  </div>
</form>

The publisher's action-xhr endpoint returns the following JSON responses:

On success:

{
  "name": "Jane Miller",
  "interests": [{"name": "Basketball"}, {"name": "Swimming"}, {"name": "Reading"}],
  "email": "email@example.com"
}

On error:

{
  "name": "Jane Miller",
  "message": "The email (email@example.com) you used is already subscribed."
}

You can render the responses in a referenced template defined earlier in the document by using the template's id as the value of the template attribute, set on the elements with the submit-success and submit-error attributes.

<template type="amp-mustache" id="submit_success_template">
  Success! Thanks {{name}} for subscribing! Please make sure to check your email {{email}}
  to confirm! After that we'll start sending you weekly articles on {{#interests}}<b>{{name}}</b> {{/interests}}.
</template>
<template type="amp-mustache" id="submit_error_template">
  Oops! {{name}}, {{message}}.
</template>

<form ...>
  <fieldset>
  ...
  </fieldset>
  <div submit-success template="submit_success_template"></div>
  <div submit-error template="submit_error_template"></div>
</form>

See the full example here.

To render a successful response with data binding

  • Use the on attribute to bind the form submit-success attribute to AMP.setState().
  • Use the event property to capture the response data.
  • Add the state attribute to the desired element to bind the form response.

The following example demonstrates a form submit-success response with amp-bind:

  <p [text]="'Thanks, ' + subscribe +'! You have successfully subscribed.'">Subscribe to our newsletter</p>
  <form method="post"
        action-xhr="/components/amp-form/submit-form-input-text-xhr"
        target="_top"
        on="submit-success: AMP.setState({'subscribe': event.response.name})">
    <div>
      <input type="text"
          name="name"
          placeholder="Name..."
          required>
      <input type="email"
        name="email"
        placeholder="Email..."
        required>
    </div>
    <input type="submit" value="Subscribe">
  </form>
 ``` 

 When the form is submitted successfully it will return a JSON response similar to the following: 


<div class="code"><pre><span></span><span class="p">{</span>
  <span class="nt">&quot;name&quot;</span><span class="p">:</span> <span class="s2">&quot;Jane Miller&quot;</span><span class="p">,</span>
  <span class="nt">&quot;email&quot;</span><span class="p">:</span> <span class="s2">&quot;email@example.com&quot;</span>
<span class="p">}</span>
</pre></div>


Then `amp-bind` updates the `<p>` element's text to match the `subscibe` state:

```html
...
  <p [text]="'Thanks, ' + subscribe +'! You have successfully subscribed.'">Thanks Jane Miller! You have successfully subscribed.</p>
...

Redirecting after a submission

You can redirect users to a new page after a successful form submission by setting the AMP-Redirect-To response header and specifying a redirect URL. The redirect URL must be a HTTPS URL, otherwise AMP will throw an error and redirection won't occur. HTTP response headers are configured via your server.

Make sure to update your Access-Control-Expose-Headers response header to include AMP-Redirect-To to the list of allowed headers. Learn more about these headers in CORS Security in AMP.

Example response headers:

AMP-Redirect-To: https://example.com/forms/thank-you
Access-Control-Expose-Headers: AMP-Access-Control-Allow-Source-Origin, AMP-Redirect-To

Custom validations

The amp-form extension allows you to build your own custom validation UI by using the custom-validation-reporting attribute along with one the following reporting strategies: show-first-on-submit, show-all-on-submit or as-you-go.

To specify custom validation on your form:

  1. Set the custom-validation-reporting attribute on your form to one of the validation reporting strategies.
  2. Provide your own validation UI marked up with special attributes. AMP will discover the special attributes and report them at the right time depending on the reporting strategy you specified.

Here's an example:

Show full code

For more examples, see examples/forms.amp.html.

For validation messages, if your element contains no text content inside, AMP will fill it out with the browser's default validation message. In the example above, when the name5 input is empty and validation is kicked off (i.e., user tried to submit the form) AMP will fill <span visible-when-invalid="valueMissing" validation-for="name5"></span> with the browser's validation message and show that span to the user.

Reporting strategies

Specify one of the following reporting options for the custom-validation-reporting attribute:

Show First on Submit

The show-first-on-submit reporting option mimics the browser's default behavior when default validation kicks in. It shows the first validation error it finds and stops there.

Show All on Submit

The show-all-on-submit reporting option shows all validation errors on all invalid inputs when the form is submitted. This is useful if you'd like to show a summary of validations.

As You Go

The as-you-go reporting option allows your user to see validation messages as they're interacting with the input. For example, if the user types an invalid email address, the user will see the error right away. Once they correct the value, the error goes away.

Interact and Submit

The interact-and-submit reporting option combines the behavior of show-all-on-submit and as-you-go. Individual fields will show any errors immediately after interactions, and on submit the form will show errors on all invalid fields.

Verification

HTML5 validation gives feedback based only on information available on the page, such as if a value matches a certain pattern. With amp-form verification you can give the user feedback that HTML5 validation alone cannot. For example, a form can use verification to check if an email address has already been registered. Another use-case is verifying that a city field and a zip code field match each other.

Here's an example:

<h4>Verification example</h4>
<form
  method="post"
  action-xhr="/form/verify-json/post"
  verify-xhr="/form/verify-json/post"
  target="_blank"
>
    <fieldset>
        <label>
            <span>Email</span>
            <input type="text" name="email" required>
        </label>
        <label>
            <span>Zip Code</span>
            <input type="tel" name="zip" required pattern="[0-9]{5}(-[0-9]{4})?">
        </label>
        <label>
            <span>City</span>
            <input type="text" name="city" required>
        </label>
        <label>
            <span>Document</span>
            <input type="file" name="document" no-verify>
        </label>
        <div class="spinner"></div>
        <input type="submit" value="Submit">
    </fieldset>
    <div submit-success>
        <template type="amp-mustache">
            <p>Congratulations! You are registered with {{email}}</p>
        </template>
    </div>
    <div submit-error>
        <template type="amp-mustache">
            {{#verifyErrors}}
                <p>{{message}}</p>
            {{/verifyErrors}}
            {{^verifyErrors}}
                <p>Something went wrong. Try again later?</p>
            {{/verifyErrors}}
        </template>
    </div>
</form>

The form sends a __amp_form_verify field as part of the form data as a hint to the server that the request is a verify request and not a formal submit. This is helpful so the server knows not to store the verify request if the same endpoint is used for verification and for submit.

Here is how an error response should look for verification:

{
  "verifyErrors": [
    {"name": "email", "message": "That email is already taken."},
    {"name": "zip", "message": "The city and zip do not match."}
  ]
}

To remove a field from the verify-xhr request, add the no-verify attribute to the input element.

For more examples, see examples/forms.amp.html.

Variable substitutions

The amp-form extension allows platform variable substitutions for inputs that are hidden and that have the data-amp-replace attribute. On each form submission, amp-form finds all input[type=hidden][data-amp-replace] inside the form and applies variable substitutions to its value attribute and replaces it with the result of the substitution.

You must provide the variables you are using for each substitution on each input by specifying a space-separated string of the variables used in data-amp-replace (see example below). AMP will not replace variables that are not explicitly specified.

Here's an example of how inputs are before and after substitutions (note that you need to use platform syntax of variable substitutions and not analytics ones):

<!-- Initial Load -->
<form ...>
  <input name="canonicalUrl" type="hidden"
        value="The canonical URL is: CANONICAL_URL - RANDOM - CANONICAL_HOSTNAME"
        data-amp-replace="CANONICAL_URL RANDOM">
  <input name="clientId" type="hidden"
        value="CLIENT_ID(myid)"
        data-amp-replace="CLIENT_ID">
  ...
</form>

Once the user tries to submit the form, AMP will try to resolve the variables and update the fields' value attribute of all fields with the appropriate substitutions. For XHR submissions, all variables are likely to be substituted and resolved. However, in non-XHR GET submissions, values that requires async-resolution might not be available due to having not been resolved previously. CLIENT_ID for example would not resolve if it wasn't resolved and cached previously.

<!-- User submits the form, variables values are resolved into fields' value -->
<form ...>
  <input name="canonicalUrl" type="hidden"
        value="The canonical URL is: https://example.com/hello - 0.242513759125 - CANONICAL_HOSTNAME"
        data-amp-replace="CANONICAL_URL RANDOM">
  <input name="clientId" type="hidden"
        value="amp:asqar893yfaiufhbas9g879ab9cha0cja0sga87scgas9ocnas0ch"
        data-amp-replace="CLIENT_ID">
    ...
</form>

Note how CANONICAL_HOSTNAME above did not get replaced because it was not in the whitelist through data-amp-replace attribute on the first field.

Substitutions will happen on every subsequent submission. Read more about variable substitutions in AMP.

Polyfills

The amp-form extension provide polyfills for behaviors and functionality missing from some browsers or being implemented in the next version of CSS.

Invalid submit blocking and validation message bubble

Browsers that use webkit-based engines currently (as of August 2016) do not support invalid form submissions. These include Safari on all platforms, and all iOS browsers. The amp-form extension polyfills this behavior to block any invalid submissions and shows validation message bubbles on invalid inputs.

User-interaction pseudo-classes

The :user-invalid and :user-valid pseudo classes are part of the future CSS Selectors 4 spec and are introduced to allow better hooks for styling invalid/valid fields based on a few criteria.

One of the main differences between :invalid and :user-invalid is when are they applied to the element. The :user-invalid class is applied after a significant interaction from the user with the field (e.g., the user types in a field, or blurs from the field).

The amp-form extension provides classes to polyfill these pseudo-classes. The amp-form extension also propagates these to ancestors fieldsetelements and form.

Styling

Classes and CSS hooks

The amp-form extension provides classes and CSS hooks for publishers to style their forms and inputs.

The following classes can be used to indicate the state of the form submission:

  • .amp-form-initial
  • .amp-form-verify
  • .amp-form-verify-error
  • .amp-form-submitting
  • .amp-form-submit-success
  • .amp-form-submit-error

The following classes are a polyfill for the user interaction pseudo classes:

  • .user-valid
  • .user-invalid

Publishers can use these classes to style their inputs and fieldsets to be responsive to user actions (e.g., highlighting an invalid input with a red border after user blurs from it).

See the full example here on using these.

Security considerations

Protecting against XSRF

In addition to following the details in the AMP CORS spec, please pay extra attention to the section on "Processing state changing requests" to protect against XSRF attacks where an attacker can execute unauthorized commands using the current user session without the user knowledge.

In general, keep in mind the following points when accepting input from the user:

  • Only use POST for state changing requests.
  • Use non-XHR GET for navigational purposes only (e.g., Search).
    • non-XHR GET requests are not going to receive accurate origin/headers and backends won't be able to protect against XSRF with the above mechanism.
    • In general, use XHR/non-XHR GET requests for navigational or information retrieval only.
  • non-XHR POST requests are not allowed in AMP documents. This is due to inconsistencies of setting Origin header on these requests across browsers. And the complications supporting it would introduce in protecting against XSRF. This might be reconsidered and introduced later, please file an issue if you think this is needed.