---
name: telnyx-fax-javascript
description: >-
  Send and receive faxes programmatically. Manage fax applications and media.
  This skill provides JavaScript SDK examples.
metadata:
  author: telnyx
  product: fax
  language: javascript
  generated_by: telnyx-ext-skills-generator
---

<!-- Auto-generated from Telnyx OpenAPI specs. Do not edit. -->

# Telnyx Fax - JavaScript

## Installation

```bash
npm install telnyx
```

## Setup

```javascript
import Telnyx from 'telnyx';

const client = new Telnyx({
  apiKey: process.env['TELNYX_API_KEY'], // This is the default and can be omitted
});
```

All examples below assume `client` is already initialized as shown above.

## Error Handling

All API calls can fail with network errors, rate limits (429), validation errors (422),
or authentication errors (401). Always handle errors in production code:

```javascript
try {
  const result = await client.messages.send({ to: '+13125550001', from: '+13125550002', text: 'Hello' });
} catch (err) {
  if (err instanceof Telnyx.APIConnectionError) {
    console.error('Network error — check connectivity and retry');
  } else if (err instanceof Telnyx.RateLimitError) {
    // 429: rate limited — wait and retry with exponential backoff
    const retryAfter = err.headers?.['retry-after'] || 1;
    await new Promise(r => setTimeout(r, retryAfter * 1000));
  } else if (err instanceof Telnyx.APIError) {
    console.error(`API error ${err.status}: ${err.message}`);
    if (err.status === 422) {
      console.error('Validation error — check required fields and formats');
    }
  }
}
```

Common error codes: `401` invalid API key, `403` insufficient permissions,
`404` resource not found, `422` validation error (check field formats),
`429` rate limited (retry with exponential backoff).

## Important Notes

- **Phone numbers** must be in E.164 format (e.g., `+13125550001`). Include the `+` prefix and country code. No spaces, dashes, or parentheses.
- **Pagination:** List methods return an auto-paginating iterator. Use `for await (const item of result) { ... }` to iterate through all pages automatically.

## List all Fax Applications

This endpoint returns a list of your Fax Applications inside the 'data' attribute of the response. You can adjust which applications are listed by using filters. Fax Applications are used to configure how you send and receive faxes using the Programmable Fax API with Telnyx.

`GET /fax_applications`

```javascript
// Automatically fetches more pages as needed.
for await (const faxApplication of client.faxApplications.list()) {
  console.log(faxApplication.id);
}
```

Returns: `active` (boolean), `anchorsite_override` (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), `application_name` (string), `created_at` (string), `id` (string), `inbound` (object), `outbound` (object), `record_type` (string), `tags` (array[string]), `updated_at` (string), `webhook_event_failover_url` (uri), `webhook_event_url` (uri), `webhook_timeout_secs` (integer | null)

## Creates a Fax Application

Creates a new Fax Application based on the parameters sent in the request. The application name and webhook URL are required. Once created, you can assign phone numbers to your application using the `/phone_numbers` endpoint.

`POST /fax_applications` — Required: `application_name`, `webhook_event_url`

Optional: `active` (boolean), `anchorsite_override` (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), `inbound` (object), `outbound` (object), `tags` (array[string]), `webhook_event_failover_url` (uri), `webhook_timeout_secs` (integer | null)

```javascript
const faxApplication = await client.faxApplications.create({
  application_name: 'fax-router',
  webhook_event_url: 'https://example.com',
});

console.log(faxApplication.data);
```

Returns: `active` (boolean), `anchorsite_override` (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), `application_name` (string), `created_at` (string), `id` (string), `inbound` (object), `outbound` (object), `record_type` (string), `tags` (array[string]), `updated_at` (string), `webhook_event_failover_url` (uri), `webhook_event_url` (uri), `webhook_timeout_secs` (integer | null)

## Retrieve a Fax Application

Return the details of an existing Fax Application inside the 'data' attribute of the response.

`GET /fax_applications/{id}`

```javascript
const faxApplication = await client.faxApplications.retrieve('1293384261075731499');

console.log(faxApplication.data);
```

Returns: `active` (boolean), `anchorsite_override` (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), `application_name` (string), `created_at` (string), `id` (string), `inbound` (object), `outbound` (object), `record_type` (string), `tags` (array[string]), `updated_at` (string), `webhook_event_failover_url` (uri), `webhook_event_url` (uri), `webhook_timeout_secs` (integer | null)

## Update a Fax Application

Updates settings of an existing Fax Application based on the parameters of the request.

`PATCH /fax_applications/{id}` — Required: `application_name`, `webhook_event_url`

Optional: `active` (boolean), `anchorsite_override` (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), `fax_email_recipient` (string | null), `inbound` (object), `outbound` (object), `tags` (array[string]), `webhook_event_failover_url` (uri), `webhook_timeout_secs` (integer | null)

```javascript
const faxApplication = await client.faxApplications.update('1293384261075731499', {
  application_name: 'fax-router',
  webhook_event_url: 'https://example.com',
});

console.log(faxApplication.data);
```

Returns: `active` (boolean), `anchorsite_override` (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), `application_name` (string), `created_at` (string), `id` (string), `inbound` (object), `outbound` (object), `record_type` (string), `tags` (array[string]), `updated_at` (string), `webhook_event_failover_url` (uri), `webhook_event_url` (uri), `webhook_timeout_secs` (integer | null)

## Deletes a Fax Application

Permanently deletes a Fax Application. Deletion may be prevented if the application is in use by phone numbers.

`DELETE /fax_applications/{id}`

```javascript
const faxApplication = await client.faxApplications.delete('1293384261075731499');

console.log(faxApplication.data);
```

Returns: `active` (boolean), `anchorsite_override` (enum: Latency, Chicago, IL, Ashburn, VA, San Jose, CA, Sydney, Australia, Amsterdam, Netherlands, London, UK, Toronto, Canada, Vancouver, Canada, Frankfurt, Germany), `application_name` (string), `created_at` (string), `id` (string), `inbound` (object), `outbound` (object), `record_type` (string), `tags` (array[string]), `updated_at` (string), `webhook_event_failover_url` (uri), `webhook_event_url` (uri), `webhook_timeout_secs` (integer | null)

## View a list of faxes

`GET /faxes`

```javascript
// Automatically fetches more pages as needed.
for await (const fax of client.faxes.list()) {
  console.log(fax.id);
}
```

Returns: `client_state` (string), `connection_id` (string), `created_at` (date-time), `direction` (enum: inbound, outbound), `from` (string), `from_display_name` (string), `id` (uuid), `media_name` (string), `media_url` (string), `preview_url` (string), `quality` (enum: normal, high, very_high, ultra_light, ultra_dark), `record_type` (enum: fax), `status` (enum: queued, media.processed, originated, sending, delivered, failed, initiated, receiving, media.processing, received), `store_media` (boolean), `stored_media_url` (string), `to` (string), `updated_at` (date-time), `webhook_failover_url` (string), `webhook_url` (string)

## Send a fax

Send a fax. Files have size limits and page count limit validations. If a file is bigger than 50MB or has more than 350 pages it will fail with `file_size_limit_exceeded` and `page_count_limit_exceeded` respectively.

`POST /faxes` — Required: `connection_id`, `from`, `to`

Optional: `black_threshold` (integer), `client_state` (string), `from_display_name` (string), `media_name` (string), `media_url` (string), `monochrome` (boolean), `preview_format` (enum: pdf, tiff), `quality` (enum: normal, high, very_high, ultra_light, ultra_dark), `store_media` (boolean), `store_preview` (boolean), `t38_enabled` (boolean), `webhook_url` (string)

```javascript
const fax = await client.faxes.create({
  connection_id: '234423',
  from: '+13125790015',
  to: '+13127367276',
    mediaUrl: 'https://example.com/document.pdf',
});

console.log(fax.data);
```

Returns: `client_state` (string), `connection_id` (string), `created_at` (date-time), `direction` (enum: inbound, outbound), `from` (string), `from_display_name` (string), `id` (uuid), `media_name` (string), `media_url` (string), `preview_url` (string), `quality` (enum: normal, high, very_high, ultra_light, ultra_dark), `record_type` (enum: fax), `status` (enum: queued, media.processed, originated, sending, delivered, failed, initiated, receiving, media.processing, received), `store_media` (boolean), `stored_media_url` (string), `to` (string), `updated_at` (date-time), `webhook_failover_url` (string), `webhook_url` (string)

## View a fax

`GET /faxes/{id}`

```javascript
const fax = await client.faxes.retrieve('182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e');

console.log(fax.data);
```

Returns: `client_state` (string), `connection_id` (string), `created_at` (date-time), `direction` (enum: inbound, outbound), `from` (string), `from_display_name` (string), `id` (uuid), `media_name` (string), `media_url` (string), `preview_url` (string), `quality` (enum: normal, high, very_high, ultra_light, ultra_dark), `record_type` (enum: fax), `status` (enum: queued, media.processed, originated, sending, delivered, failed, initiated, receiving, media.processing, received), `store_media` (boolean), `stored_media_url` (string), `to` (string), `updated_at` (date-time), `webhook_failover_url` (string), `webhook_url` (string)

## Delete a fax

`DELETE /faxes/{id}`

```javascript
await client.faxes.delete('182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e');
```

## Cancel a fax

Cancel the outbound fax that is in one of the following states: `queued`, `media.processed`, `originated` or `sending`

`POST /faxes/{id}/actions/cancel`

```javascript
const response = await client.faxes.actions.cancel('182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e');

console.log(response.data);
```

Returns: `result` (string)

## Refresh a fax

Refreshes the inbound fax's media_url when it has expired

`POST /faxes/{id}/actions/refresh`

```javascript
const response = await client.faxes.actions.refresh('182bd5e5-6e1a-4fe4-a799-aa6d9a6ab26e');

console.log(response.data);
```

Returns: `result` (string)

---

## Webhooks

### Webhook Verification

Telnyx signs webhooks with Ed25519. Each request includes `telnyx-signature-ed25519`
and `telnyx-timestamp` headers. Always verify signatures in production:

```javascript
// In your webhook handler (e.g., Express — use raw body, not parsed JSON):
app.post('/webhooks', express.raw({ type: 'application/json' }), async (req, res) => {
  try {
    const event = await client.webhooks.unwrap(req.body.toString(), {
      headers: req.headers,
    });
    // Signature valid — event is the parsed webhook payload
    console.log('Received event:', event.data.event_type);
    res.status(200).send('OK');
  } catch (err) {
    console.error('Webhook verification failed:', err.message);
    res.status(400).send('Invalid signature');
  }
});
```

The following webhook events are sent to your configured webhook URL.
All webhooks include `telnyx-timestamp` and `telnyx-signature-ed25519` headers for Ed25519 signature verification. Use `client.webhooks.unwrap()` to verify.

| Event | Description |
|-------|-------------|
| `fax.delivered` | Fax Delivered |
| `fax.failed` | Fax Failed |
| `fax.media.processed` | Fax Media Processed |
| `fax.queued` | Fax Queued |
| `fax.sending.started` | Fax Sending Started |

### Webhook payload fields

**`fax.delivered`**

| Field | Type | Description |
|-------|------|-------------|
| `data.record_type` | enum: event | Identifies the type of the resource. |
| `data.id` | uuid | Identifies the type of resource. |
| `data.occurred_at` | date-time | ISO 8601 datetime of when the event occurred. |
| `data.event_type` | enum: fax.delivered | The type of event being delivered. |
| `data.payload.call_duration_secs` | integer | The duration of the call in seconds. |
| `data.payload.connection_id` | string | The ID of the connection used to send the fax. |
| `data.payload.direction` | enum: inbound, outbound | The direction of the fax. |
| `data.payload.fax_id` | uuid | Identifies the fax. |
| `data.payload.original_media_url` | string | The original URL to the PDF used for the fax's media. |
| `data.payload.media_name` | string | The media_name used for the fax's media. |
| `data.payload.to` | string | The phone number, in E.164 format, the fax will be sent to or SIP URI |
| `data.payload.from` | string | The phone number, in E.164 format, the fax will be sent from. |
| `data.payload.user_id` | uuid | Identifier of the user to whom the fax belongs |
| `data.payload.page_count` | integer | Number of transferred pages |
| `data.payload.status` | enum: delivered | The status of the fax. |
| `data.payload.client_state` | string | State received from a command. |
| `meta.attempt` | integer | The delivery attempt number. |
| `meta.delivered_to` | uri | The URL the webhook was delivered to. |

**`fax.failed`**

| Field | Type | Description |
|-------|------|-------------|
| `data.record_type` | enum: event | Identifies the type of the resource. |
| `data.id` | uuid | Identifies the type of resource. |
| `data.occurred_at` | date-time | ISO 8601 datetime of when the event occurred. |
| `data.event_type` | enum: fax.failed | The type of event being delivered. |
| `data.payload.connection_id` | string | The ID of the connection used to send the fax. |
| `data.payload.direction` | enum: inbound, outbound | The direction of the fax. |
| `data.payload.fax_id` | uuid | Identifies the fax. |
| `data.payload.original_media_url` | string | The original URL to the PDF used for the fax's media. |
| `data.payload.media_name` | string | The media_name used for the fax's media. |
| `data.payload.to` | string | The phone number, in E.164 format, the fax will be sent to or SIP URI |
| `data.payload.from` | string | The phone number, in E.164 format, the fax will be sent from. |
| `data.payload.user_id` | uuid | Identifier of the user to whom the fax belongs |
| `data.payload.failure_reason` | enum: rejected | Cause of the sending failure |
| `data.payload.status` | enum: failed | The status of the fax. |
| `data.payload.client_state` | string | State received from a command. |
| `meta.attempt` | integer | The delivery attempt number. |
| `meta.delivered_to` | uri | The URL the webhook was delivered to. |

**`fax.media.processed`**

| Field | Type | Description |
|-------|------|-------------|
| `data.record_type` | enum: event | Identifies the type of the resource. |
| `data.id` | uuid | Identifies the type of resource. |
| `data.occurred_at` | date-time | ISO 8601 datetime of when the event occurred. |
| `data.event_type` | enum: fax.media.processed | The type of event being delivered. |
| `data.payload.connection_id` | string | The ID of the connection used to send the fax. |
| `data.payload.direction` | enum: inbound, outbound | The direction of the fax. |
| `data.payload.fax_id` | uuid | Identifies the fax. |
| `data.payload.original_media_url` | string | The original URL to the PDF used for the fax's media. |
| `data.payload.media_name` | string | The media_name used for the fax's media. |
| `data.payload.to` | string | The phone number, in E.164 format, the fax will be sent to or SIP URI |
| `data.payload.from` | string | The phone number, in E.164 format, the fax will be sent from. |
| `data.payload.user_id` | uuid | Identifier of the user to whom the fax belongs |
| `data.payload.status` | enum: media.processed | The status of the fax. |
| `data.payload.client_state` | string | State received from a command. |
| `meta.attempt` | integer | The delivery attempt number. |
| `meta.delivered_to` | uri | The URL the webhook was delivered to. |

**`fax.queued`**

| Field | Type | Description |
|-------|------|-------------|
| `data.record_type` | enum: event | Identifies the type of the resource. |
| `data.id` | uuid | Identifies the type of resource. |
| `data.occurred_at` | date-time | ISO 8601 datetime of when the event occurred. |
| `data.event_type` | enum: fax.queued | The type of event being delivered. |
| `data.payload.connection_id` | string | The ID of the connection used to send the fax. |
| `data.payload.direction` | enum: inbound, outbound | The direction of the fax. |
| `data.payload.fax_id` | uuid | Identifies the fax. |
| `data.payload.original_media_url` | string | The original URL to the PDF used for the fax's media. |
| `data.payload.media_name` | string | The media_name used for the fax's media. |
| `data.payload.to` | string | The phone number, in E.164 format, the fax will be sent to or SIP URI |
| `data.payload.from` | string | The phone number, in E.164 format, the fax will be sent from. |
| `data.payload.user_id` | uuid | Identifier of the user to whom the fax belongs |
| `data.payload.status` | enum: queued | The status of the fax. |
| `data.payload.client_state` | string | State received from a command. |
| `meta.attempt` | integer | The delivery attempt number. |
| `meta.delivered_to` | uri | The URL the webhook was delivered to. |

**`fax.sending.started`**

| Field | Type | Description |
|-------|------|-------------|
| `data.record_type` | enum: event | Identifies the type of the resource. |
| `data.id` | uuid | Identifies the type of resource. |
| `data.occurred_at` | date-time | ISO 8601 datetime of when the event occurred. |
| `data.event_type` | enum: fax.sending.started | The type of event being delivered. |
| `data.payload.connection_id` | string | The ID of the connection used to send the fax. |
| `data.payload.direction` | enum: inbound, outbound | The direction of the fax. |
| `data.payload.fax_id` | uuid | Identifies the fax. |
| `data.payload.original_media_url` | string | The original URL to the PDF used for the fax's media. |
| `data.payload.media_name` | string | The media_name used for the fax's media. |
| `data.payload.to` | string | The phone number, in E.164 format, the fax will be sent to or SIP URI |
| `data.payload.from` | string | The phone number, in E.164 format, the fax will be sent from. |
| `data.payload.user_id` | uuid | Identifier of the user to whom the fax belongs |
| `data.payload.status` | enum: sending | The status of the fax. |
| `data.payload.client_state` | string | State received from a command. |
| `meta.attempt` | integer | The delivery attempt number. |
| `meta.delivered_to` | uri | The URL the webhook was delivered to. |