JavaScript SDK

Installation

You can install the package from npm:

npm install loops

Minimum Node version required: 18.0.0. You will need a Loops API key to use the package. In your Loops account, go to the API Settings page and click Generate key. Copy this key and save it in your application code (for example as LOOPS_API_KEY in an .env file).

Next.js guide

Read our guide for sending email from Next.js projects.

Usage

import { LoopsClient, APIError } from "loops";

const loops = new LoopsClient(process.env.LOOPS_API_KEY);

try {
  const resp = await loops.createContact("[email protected]");
  // resp.success and resp.id available when successful
} catch (error) {
  if (error instanceof APIError) {
    // JSON returned by the API is in error.json and the HTTP code is in error.statusCode
    // Error messages explaining the issue can be found in error.json.message
    console.log(error.json);
    console.log(error.statusCode);
  } else {
    // Non-API errors
  }
}

Handling rate limits

If you import RateLimitExceededError you can check for rate limit issues with your requests. You can access details about the rate limits from the limit and remaining attributes.

import { LoopsClient, APIError, RateLimitExceededError } from "loops";

const loops = new LoopsClient(process.env.LOOPS_API_KEY);

try {
  const resp = await loops.createContact("[email protected]");
} catch (error) {
  if (error instanceof RateLimitExceededError) {
    console.log(`Rate limit exceeded (${error.limit} per second)`);
    // Code here to re-try this request
  } else {
    // Handle other errors
  }
}

Default contact properties

Each contact in Loops has a set of default properties. These will always be returned in API results.

id
email
firstName
lastName
source
subscribed
userGroup
userId
optInStatus

Custom contact properties

You can use custom contact properties in API calls. Please make sure to add custom properties in your Loops account before using them with the SDK.

testApiKey()

Test that an API key is valid. API Reference

Parameters

None

Example

const resp = await loops.testApiKey();

Response

{
  "success": true,
  "teamName": "My team"
}

Error handling is done through the APIError class, which provides statusCode and json properties containing the API’s error response details. For implementation examples, see the Usage section.

HTTP 401 Unauthorized
{
  "error": "Invalid API key"
}

createContact()

Create a new contact. API Reference

Parameters

Name	Type	Required	Notes
`email`	string	Yes	If a contact already exists with this email address, an error response will be returned.
`properties`	object	No	An object containing default and any custom properties for your contact. Please add custom properties in your Loops account before using them with the SDK. Values can be of type `string`, `number`, `null` (to reset a value), `boolean` or `date` (see allowed date formats).
`mailingLists`	object	No	An object of mailing list IDs and boolean subscription statuses.

Examples

const resp = await loops.createContact({ email: "[email protected]" });

const contactProperties = {
  firstName: "Bob" /* Default property */,
  favoriteColor: "Red" /* Custom property */,
};
const mailingLists = {
  cm06f5v0e45nf0ml5754o9cix: true /* Subscribe */,
  cm16k73gq014h0mmj5b6jdi9r: false /* Unsubscribe */,
};
const resp = await loops.createContact({
  email: "[email protected]",
  properties: contactProperties,
  mailingLists,
});

Response

{
  "success": true,
  "id": "id_of_contact"
}

HTTP 400 Bad Request
{
  "success": false,
  "message": "An error message here."
}

updateContact()

Update a contact. This method will create a contact if one doesn’t already exist. Note: To update a contact’s email address, the contact requires a userId value. Then you can make a request with their userId and an updated email address. API Reference

Parameters

Name	Type	Required	Notes
`email`	string	No	The email address of the contact to update. If there is no contact with this email address, a new contact will be created using the email and properties in this request. Required if `userId` is not present.
`userId`	string	No	The contact’s unique user ID. If you use `userId` without `email`, this value must have already been added to your contact in Loops. Required if `email` is not present.
`properties`	object	No	An object containing default and any custom properties for your contact. Please add custom properties in your Loops account before using them with the SDK. Values can be of type `string`, `number`, `null` (to reset a value), `boolean` or `date` (see allowed date formats).
`mailingLists`	object	No	An object of mailing list IDs and boolean subscription statuses.

Example

const resp = await loops.updateContact({
  email: "[email protected]",
  properties: {
    firstName: "Bob" /* Default property */,
    favoriteColor: "Blue" /* Custom property */,
  },
});

/* Updating a contact's email address using userId */
const resp = await loops.updateContact({
  userId: "1234",
  email: "[email protected]",
});

/* Subscribe a contact to a mailing list */
const resp = await loops.updateContact({
  email: "[email protected]",
  mailingLists: {
    cm06f5v0e45nf0ml5754o9cix: true,
  },
});

Response

{
  "success": true,
  "id": "id_of_contact"
}

HTTP 400 Bad Request
{
  "success": false,
  "message": "An error message here."
}

findContact()

Find a contact. API Reference

Parameters

You must use one parameter in the request.

Name	Type	Required	Notes
`email`	string	No
`userId`	string	No

Examples

const resp = await loops.findContact({ email: "[email protected]" });

const resp = await loops.findContact({ userId: "12345" });

Response

This method will return a list containing a single contact object, which will include all default properties and any custom properties. If no contact is found, an empty list will be returned.

[
  {
    "id": "cll6b3i8901a9jx0oyktl2m4u",
    "email": "[email protected]",
    "firstName": "Bob",
    "lastName": null,
    "source": "API",
    "subscribed": true,
    "userGroup": "",
    "userId": "12345",
    "mailingLists": {
      "cm06f5v0e45nf0ml5754o9cix": true
    },
    "optInStatus": null,
    "favoriteColor": "Blue" /* Custom property */
  }
]

deleteContact()

Delete a contact, either by email address or userId. API Reference

Parameters

You must use one parameter in the request.

Name	Type	Required	Notes
`email`	string	No
`userId`	string	No

Example

const resp = await loops.deleteContact({ email: "[email protected]" });

const resp = await loops.deleteContact({ userId: "12345" });

Response

{
  "success": true,
  "message": "Contact deleted."
}

HTTP 400 Bad Request
{
  "success": false,
  "message": "An error message here."
}

HTTP 404 Not Found
{
  "success": false,
  "message": "An error message here."
}

createContactProperty()

Create a new contact property. API Reference

Parameters

Name	Type	Required	Notes
`name`	string	Yes	The name of the property. Should be in camelCase, like `planName` or `favouriteColor`.
`type`	string	Yes	The property’s value type. Can be one of `string`, `number`, `boolean` or `date`.

Examples

const resp = await loops.createContactProperty("planName", "string");

Response

{
  "success": true
}

HTTP 400 Bad Request
{
  "success": false,
  "message": "An error message here."
}

getContactProperties()

Get a list of your account’s contact properties. API Reference

Parameters

Name	Type	Required	Notes
`list`	string	No	Use “custom” to retrieve only your account’s custom properties.

Example

const resp = await loops.getContactProperties();

const resp = await loops.getContactProperties("custom");

Response

This method will return a list of contact property objects containing key, label and type attributes.

[
  {
    "key": "firstName",
    "label": "First Name",
    "type": "string"
  },
  {
    "key": "lastName",
    "label": "Last Name",
    "type": "string"
  },
  {
    "key": "email",
    "label": "Email",
    "type": "string"
  },
  {
    "key": "notes",
    "label": "Notes",
    "type": "string"
  },
  {
    "key": "source",
    "label": "Source",
    "type": "string"
  },
  {
    "key": "userGroup",
    "label": "User Group",
    "type": "string"
  },
  {
    "key": "userId",
    "label": "User Id",
    "type": "string"
  },
  {
    "key": "subscribed",
    "label": "Subscribed",
    "type": "boolean"
  },
  {
    "key": "createdAt",
    "label": "Created At",
    "type": "date"
  },
  {
    "key": "favoriteColor",
    "label": "Favorite Color",
    "type": "string"
  },
  {
    "key": "plan",
    "label": "Plan",
    "type": "string"
  }
]

getMailingLists()

Get a list of your account’s mailing lists. Read more about mailing lists API Reference

Parameters

None

Example

const resp = await loops.getMailingLists();

Response

This method will return a list of mailing list objects containing id, name, description and isPublic attributes. If your account has no mailing lists, an empty list will be returned.

[
  {
    "id": "cm06f5v0e45nf0ml5754o9cix",
    "name": "Main list",
    "description": "All customers.",
    "isPublic": true
  },
  {
    "id": "cm16k73gq014h0mmj5b6jdi9r",
    "name": "Investors",
    "description": null,
    "isPublic": false
  }
]

sendEvent()

Send an event to trigger an email in Loops. Read more about events API Reference

Parameters

Name	Type	Required	Notes
`email`	string	No	The contact’s email address. Required if `userId` is not present.
`userId`	string	No	The contact’s unique user ID. If you use `userId` without `email`, this value must have already been added to your contact in Loops. Required if `email` is not present.
`eventName`	string	Yes
`contactProperties`	object	No	An object containing contact properties, which will be updated or added to the contact when the event is received. Please add custom properties in your Loops account before using them with the SDK. Values can be of type `string`, `number`, `null` (to reset a value), `boolean` or `date` (see allowed date formats).
`eventProperties`	object	No	An object containing event properties, which will be made available in emails that are triggered by this event. Values can be of type `string`, `number`, `boolean` or `date` (see allowed date formats).
`mailingLists`	object	No	An object of mailing list IDs and boolean subscription statuses.
`headers`	object	No	Additional headers to send with the request.

Examples

const resp = await loops.sendEvent({
  email: "[email protected]",
  eventName: "signup",
});

const resp = await loops.sendEvent({
  email: "[email protected]",
  eventName: "signup",
  eventProperties: {
    username: "user1234",
    signupDate: "2024-03-21T10:09:23Z",
  },
  mailingLists: {
    cm06f5v0e45nf0ml5754o9cix: true,
    cm16k73gq014h0mmj5b6jdi9r: false,
  },
});

// In this case with both email and userId present, the system will look for a contact with either a
//  matching `email` or `userId` value.
// If a contact is found for one of the values (e.g. `email`), the other value (e.g. `userId`) will be updated.
// If a contact is not found, a new contact will be created using both `email` and `userId` values.
// Any values added in `contactProperties` will also be updated on the contact.
const resp = await loops.sendEvent({
  userId: "1234567890",
  email: "[email protected]",
  eventName: "signup",
  contactProperties: {
    firstName: "Bob",
    plan: "pro",
  },
});

// Example with Idempotency-Key header
const resp = await loops.sendEvent({
  email: "[email protected]",
  eventName: "signup",
  headers: {
    "Idempotency-Key": "550e8400-e29b-41d4-a716-446655440000",
  },
});

Response

{
  "success": true
}

HTTP 400 Bad Request
{
  "success": false,
  "message": "An error message here."
}

sendTransactionalEmail()

Send a transactional email to a contact. Learn about sending transactional email API Reference

Parameters

Name	Type	Required	Notes
`transactionalId`	string	Yes	The ID of the transactional email to send.
`email`	string	Yes	The email address of the recipient.
`addToAudience`	boolean	No	If `true`, a contact will be created in your audience using the `email` value (if a matching contact doesn’t already exist).
`dataVariables`	object	No	An object containing data as defined by the data variables added to the transactional email template. Values can be of type `string` or `number`.
`attachments`	object[]	No	A list of attachments objects. Please note: Attachments need to be enabled on your account before using them with the API. Read more
`attachments[].filename`	string	No	The name of the file, shown in email clients.
`attachments[].contentType`	string	No	The MIME type of the file.
`attachments[].data`	string	No	The base64-encoded content of the file.
`headers`	object	No	Additional headers to send with the request.

Examples

const resp = await loops.sendTransactionalEmail({
  transactionalId: "clfq6dinn000yl70fgwwyp82l",
  email: "[email protected]",
  dataVariables: {
    loginUrl: "https://myapp.com/login/",
  },
});

// Example with Idempotency-Key header
const resp = await loops.sendTransactionalEmail({
  transactionalId: "clfq6dinn000yl70fgwwyp82l",
  email: "[email protected]",
  dataVariables: {
    loginUrl: "https://myapp.com/login/",
  },
  headers: {
    "Idempotency-Key": "550e8400-e29b-41d4-a716-446655440000",
  },
});

// Please contact us to enable attachments on your account.
const resp = await loops.sendTransactionalEmail({
  transactionalId: "clfq6dinn000yl70fgwwyp82l",
  email: "[email protected]",
  dataVariables: {
    loginUrl: "https://myapp.com/login/",
  },
  attachments: [
    {
      filename: "presentation.pdf",
      contentType: "application/pdf",
      data: "JVBERi0xLjMKJcTl8uXrp/Og0MTGCjQgMCBvYmoKPD...",
    },
  ],
});

Response

{
  "success": true
}

HTTP 400 Bad Request
{
  "success": false,
  "path": "dataVariables",
  "message": "There are required fields for this email. You need to include a 'dataVariables' object with the required fields."
}

HTTP 400 Bad Request
{
  "success": false,
  "error": {
    "path": "dataVariables",
    "message": "Missing required fields: login_url"
  },
  "transactionalId": "clfq6dinn000yl70fgwwyp82l"
}

getTransactionalEmails()

Get a list of published transactional emails. API Reference

Parameters

Name	Type	Required	Notes
`perPage`	integer	No	How many results to return per page. Must be between 10 and 50. Defaults to 20 if omitted.
`cursor`	string	No	A cursor, to return a specific page of results. Cursors can be found from the `pagination.nextCursor` value in each response.

Example

const resp = await loops.getTransactionalEmails();

const resp = await loops.getTransactionalEmails({ perPage: 15 });

Response

{
  "pagination": {
    "totalResults": 23,
    "returnedResults": 20,
    "perPage": 20,
    "totalPages": 2,
    "nextCursor": "clyo0q4wo01p59fsecyxqsh38",
    "nextPage": "https://app.loops.so/api/v1/transactional?cursor=clyo0q4wo01p59fsecyxqsh38&perPage=20"
  },
  "data": [
    {
      "id": "clfn0k1yg001imo0fdeqg30i8",
      "lastUpdated": "2023-11-06T17:48:07.249Z",
      "dataVariables": []
    },
    {
      "id": "cll42l54f20i1la0lfooe3z12",
      "lastUpdated": "2025-02-02T02:56:28.845Z",
      "dataVariables": [
        "confirmationUrl"
      ]
    },
    {
      "id": "clw6rbuwp01rmeiyndm80155l",
      "lastUpdated": "2024-05-14T19:02:52.000Z",
      "dataVariables": [
        "firstName",
        "lastName",
        "inviteLink"
      ]
    },
    ...
  ]
}

Version history

v6.0.1 (Oct 15, 2025) - Added optInStatus to contact object in findContact() for the new double opt-in feature.
v6.0.0 (Aug 22, 2025) - createContact() and updateContact() now have a single object parameter instead of named parameters (breaking change). This allows support for using either email or userId when updating contacts.
v5.0.1 (May 13, 2025) - Added a headers parameter for sendEvent() and sendTransactionalEmail(), enabling support for the Idempotency-Key header.
v5.0.0 (Apr 29, 2025)
- Types are now exported so you can use them in your application.
- ValidationError is now thrown when parameters are not added correctly.
- Error is now returned if the API key is missing.
- Added tests.
v4.1.0 (Feb 27, 2025) - Support for new List transactional emails endpoint.
v4.0.0 (Jan 16, 2025)
- Added APIError to more easily understand API errors. See usage example.
- Added support for two new contact property endpoints: List contact properties and Create contact property.
- Deprecated and removed the getCustomFields() method (you can now use listContactProperties() instead).
v3.4.1 (Dec 18, 2024) - Support for a new description attribute in getMailingLists().
v3.4.0 (Oct 29, 2024) - Added rate limit handling with RateLimitExceededError.
v3.3.0 (Sep 9, 2024) - Added testApiKey() method.
v3.2.0 (Aug 23, 2024) - Added support for a new mailingLists attribute in findContact().
v3.1.1 (Aug 16, 2024) - Support for a new isPublic attribute in getMailingLists().
v3.1.0 (Aug 12, 2024) - The SDK now accepts null as a value for contact properties in createContact(), updateContact() and sendEvent(), which allows you to reset/empty properties.
v3.0.0 (Jul 2, 2024) - sendTransactionalEmail() now accepts an object instead of separate parameters (breaking change).
v2.2.0 (Jul 2, 2024) - Deprecated. Added new addToAudience option to sendTransactionalEmail().
v2.1.1 (Jun 20, 2024) - Added support for mailing lists in createContact(), updateContact() and sendEvent().
v2.1.0 (Jun 19, 2024) - Added support for new List mailing lists endpoint.
v2.0.0 (Apr 19, 2024)
- Added userId as a parameter to findContact(). This includes a breaking change for the findContact() parameters.
- userId values must now be strings (could have also been numbers previously).
v1.0.1 (Apr 1, 2024) - Fixed types for sendEvent().
v1.0.0 (Mar 28, 2024) - Fix for ESM types. Switched to named export.
v0.4.0 (Mar 22, 2024) - Support for new eventProperties in sendEvent(). This includes a breaking change for the sendEvent() parameters.
v0.3.0 (Feb 22, 2024) - Updated minimum Node version to 18.0.0.
v0.2.1 (Feb 6, 2024) - Fix for ESM imports.
v0.2.0 (Feb 1, 2024) - CommonJS support.
v0.1.5 (Jan 25, 2024) - getCustomFields() now returns type values for each contact property.
v0.1.4 (Jan 25, 2024) - Added support for userId in sendEvent() request. Added missing error response type for sendEvent() requests.
v0.1.3 (Dec 8, 2023) - Added support for transactional attachments.
v0.1.2 (Dec 6, 2023) - Improved transactional error types.
v0.1.1 (Nov 1, 2023) - Initial release.

Contributing

Bug reports and pull requests are welcome at github.com/Loops-so/loops-js. Please read our Contributing Guidelines.

Learn

API

Guides

​Installation

Next.js guide

​Usage

​Handling rate limits

​Default contact properties

​Custom contact properties

​Methods

​testApiKey()

​Parameters

​Example

​Response

​createContact()

​Parameters

​Examples

​Response

​updateContact()

​Parameters

​Example

​Response

​findContact()

​Parameters

​Examples

​Response

​deleteContact()

​Parameters

​Example

​Response

​createContactProperty()

​Parameters

​Examples

​Response

​getContactProperties()

​Parameters

​Example

​Response

​getMailingLists()

​Parameters

​Example

​Response

​sendEvent()

​Parameters

​Examples

​Response

​sendTransactionalEmail()

​Parameters

​Examples

​Response

​getTransactionalEmails()

​Parameters

​Example

​Response

​Version history

​Contributing

Installation

Usage

Handling rate limits

Default contact properties

Custom contact properties

Methods

testApiKey()

Parameters

Example

Response

createContact()

Parameters

Examples

Response

updateContact()

Parameters

Example

Response

findContact()

Parameters

Examples

Response

deleteContact()

Parameters

Example

Response

createContactProperty()

Parameters

Examples

Response

getContactProperties()

Parameters

Example

Response

getMailingLists()

Parameters

Example

Response

sendEvent()

Parameters

Examples

Response

sendTransactionalEmail()

Parameters

Examples

Response

getTransactionalEmails()

Parameters

Example

Response

Version history

Contributing