Forminit JS SDK Reference

The official JavaScript/TypeScript SDK for Forminit form backend service.

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Installation

# npm
npm install forminit

# yarn
yarn add forminit

# pnpm
pnpm add forminit

CDN (Browser)

<script src="https://forminit.com/sdk/v1/forminit.js"></script>

---

Quick Start

Browser (with Proxy)

const forminit = new Forminit({ proxyUrl: '/api/forminit' });

const form = document.getElementById('contact-form');
form.addEventListener('submit', async (e) => {
  e.preventDefault();
  
  const formData = new FormData(form);
  const { data, error } = await forminit.submit('YOUR_FORM_ID', formData);
  
  if (error) {
    console.error(error.message);
    return;
  }
  
  console.log('Submission ID:', data.hashId);
});

Server-side (Node.js)

For Express and other Node.js backends, see the Node.js guide.

import { Forminit } from 'forminit';

const forminit = new Forminit({
  apiKey: process.env.FORMINIT_API_KEY,
});

const { data, error } = await forminit.submit('YOUR_FORM_ID', {
  blocks: [
    {
      type: 'sender',
      properties: {
        email: 'john@example.com',
        firstName: 'John',
        lastName: 'Doe',
      },
    },
    {
      type: 'text',
      name: 'message',
      value: 'Hello world',
    },
  ],
});

---

Configuration

Option	Type	Description
proxyUrl	string	Client-side proxy URL to protect API key
apiKey	string	Server-side API key for authentication

Client-side:

const forminit = new Forminit({ proxyUrl: '/api/forminit' });

Server-side:

const forminit = new Forminit({ apiKey: process.env.FORMINIT_API_KEY });

---

Class: Forminit

Constructor

new Forminit(config?)

Options:

Option	Type	Description
proxyUrl	string	Client-side proxy URL to protect API key
apiKey	string	Server-side API key for authentication

Methods

submit()

forminit.submit(formId, data)

Submits form data to Forminit.

Parameters:

Parameter	Type	Description
formId	string	Your Forminit form ID
data	FormData or object	Form data to submit

Returns: Promise with { data, redirectUrl, error }

setUserInfo()

forminit.setUserInfo({ ip, userAgent, referer })

Sets user information for server-side submissions. Used when submitting on behalf of a user.

Parameters:

Parameter	Type	Description
ip	string	User’s IP address
userAgent	string	User’s browser user agent
referer	string	Referring page URL

---

Submission Formats

FormData

Use standard HTML form field naming with the fi- prefix:

<form id="contact-form">
  <input type="email" name="fi-sender-email" required />
  <input type="text" name="fi-sender-firstName" required />
  <input type="text" name="fi-sender-lastName" required />
  <textarea name="fi-text-message" required></textarea>
  <button type="submit">Send</button>
</form>

Field Naming Patterns:

Block Type	Pattern	Example
Sender properties	fi-sender-{property}	fi-sender-email
Text	fi-text-{name}	fi-text-message
Number	fi-number-{name}	fi-number-quantity
Email	fi-email-{name}	fi-email-invitee
Phone	fi-phone-{name}	fi-phone-emergency
URL	fi-url-{name}	fi-url-website
Date	fi-date-{name}	fi-date-appointment
Rating	fi-rating-{name}	fi-rating-satisfaction
Select	fi-select-{name}	fi-select-plan
Radio	fi-radio-{name}	fi-radio-priority
Checkbox	fi-checkbox-{name}	fi-checkbox-features
File	fi-file-{name}	fi-file-resume
Country	fi-country-{name}	fi-country-shipping

JSON

{
  blocks: [
    {
      type: 'sender',
      properties: {
        email: 'john@example.com',
        firstName: 'John',
        lastName: 'Doe',
      },
    },
    {
      type: 'text',
      name: 'message',
      value: 'Hello world',
    },
  ],
}

Note: JSON submissions do not support file uploads. Use FormData for forms with files.

---

Block Types

Sender Block (Object Block)

Collects submitter information. Can only appear once per submission.

{
  type: 'sender',
  properties: {
    email?: string;       // Email address
    firstName?: string;   // First name
    lastName?: string;    // Last name
    fullName?: string;    // Full name
    phone?: string;       // Phone (E.164 format)
    userId?: string;      // User ID from your system
    company?: string;     // Company name
    position?: string;    // Job title
    address?: string;     // Street address
    city?: string;        // City
    country?: string;     // Country (ISO alpha-2)
    title?: string;       // Title (Mr, Mrs, Dr, Prof)
  }
}

At least one of userId, email, phone, firstName, lastName, or fullName is required.

Tracking Block (Object Block)

Captures UTM parameters and attribution data. Can only appear once per submission.

{
  type: 'tracking',
  properties: {
    utmSource?: string;
    utmMedium?: string;
    utmCampaign?: string;
    utmTerm?: string;
    utmContent?: string;
    referrer?: string;
    gclid?: string;       // Google Ads
    fbclid?: string;      // Facebook
    msclkid?: string;     // Microsoft Ads
    ttclid?: string;      // TikTok
    // ... other ad platform IDs
  }
}

Note: The SDK automatically captures UTM parameters from the URL on client-side.

Field Blocks

Each field block requires a unique name identifier.

// Text
{ type: 'text', name: 'message', value: 'Hello world' }

// Number
{ type: 'number', name: 'quantity', value: 10 }

// Email
{ type: 'email', name: 'invitee', value: 'friend@example.com' }

// Phone (E.164 format)
{ type: 'phone', name: 'emergency', value: '+12025550123' }

// URL
{ type: 'url', name: 'website', value: 'https://example.com' }

// Date (ISO 8601)
{ type: 'date', name: 'appointment', value: '2025-01-15' }

// Rating (1-5)
{ type: 'rating', name: 'satisfaction', value: 5 }

// Select (dropdown single or multi)
{ type: 'select', name: 'plan', value: 'Pro' }
{ type: 'select', name: 'services', value: ['web', 'seo'] }

// Radio (single choice)
{ type: 'radio', name: 'priority', value: 'high' }

// Checkbox (single or multi-choice)
{ type: 'checkbox', name: 'newsletter', value: 'yes' }
{ type: 'checkbox', name: 'features', value: ['api', 'support'] }

// Country (ISO 3166-1 alpha-2)
{ type: 'country', name: 'shipping', value: 'US' }

---

Response

Success Response

{
  "data": {
    "hashId": "7LMIBoYY74JOCp1k",
    "date": "2026-01-01 21:10:24",
    "blocks": {
      "sender": {
        "firstName": "John",
        "lastName": "Doe",
        "email": "john@example.com"
      },
      "message": "Hello world"
    }
  },
  "redirectUrl": "https://forminit.com/thank-you"
}

Field	Type	Description
data.hashId	string	Unique submission identifier
data.date	string	Submission timestamp
data.blocks	object	Submitted field values
redirectUrl	string	Thank you page URL

Error Response

{
  "error": {
    "success": false,
    "error": "FI_SCHEMA_FORMAT_EMAIL",
    "code": 400,
    "message": "Invalid email format"
  }
}

Field	Type	Description
error.error	string	Error code
error.code	number	HTTP status code
error.message	string	Human-readable message

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Framework Integrations

Next.js

Create an API route to proxy requests:

// app/api/forminit/route.ts
import { createForminitProxy } from 'forminit/next';

const forminit = createForminitProxy({
  apiKey: process.env.FORMINIT_API_KEY!,
});

export const POST = forminit.POST;

Use in your component:

'use client';

import { Forminit } from 'forminit';

const forminit = new Forminit({ proxyUrl: '/api/forminit' });

// Submit form...

Nuxt.js

Create a server API route:

// server/api/forminit.post.ts
import { createForminitNuxtHandler } from 'forminit/nuxt';

const config = useRuntimeConfig();

export default defineEventHandler(
  createForminitNuxtHandler({
    apiKey: config.forminitApiKey,
  })
);

Configure runtime config:

// nuxt.config.ts
export default defineNuxtConfig({
  runtimeConfig: {
    forminitApiKey: process.env.FORMINIT_API_KEY,
  },
});

Use in your component:

import { Forminit } from 'forminit';

const forminit = new Forminit({ proxyUrl: '/api/forminit' });

// Submit form...

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Automatic Tracking

On client-side, the SDK automatically captures URL parameters:

URL Parameter	Captured As
utm_source	utmSource
utm_medium	utmMedium
utm_campaign	utmCampaign
utm_term	utmTerm
utm_content	utmContent
gclid	gclid
fbclid	fbclid
msclkid	msclkid
ttclid	ttclid
twclid	twclid

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Error Codes

Error Code	Status	Description
MISSING_API_KEY	401	Server-side call without API key
FORM_NOT_FOUND	404	Form ID does not exist
FORM_DISABLED	403	Form is currently disabled
EMPTY_SUBMISSION	400	No fields with values submitted
FI_SCHEMA_FORMAT_EMAIL	400	Invalid email format
FI_RULES_PHONE_INVALID	400	Invalid phone number format
FI_SCHEMA_RANGE_RATING	400	Rating not between 1-5
FI_DATA_COUNTRY_INVALID	400	Invalid country code
TOO_MANY_REQUESTS	429	Rate limit exceeded

---

TypeScript Support

The SDK includes full TypeScript definitions:

import { Forminit } from 'forminit';

const forminit = new Forminit({ proxyUrl: '/api/forminit' });

const { data, error } = await forminit.submit('form-id', formData);

if (data) {
  console.log(data.hashId); // string
  console.log(data.date);   // string
  console.log(data.blocks); // object
}

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Rate Limits

Authentication	Rate Limit
With API Key	5 requests per second per IP address
Without API Key	1 request per 5 seconds per IP address

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Best Practices

1. Never expose API keys in client-side code. Use a server-side proxy.
2. Use FormData for file uploads. JSON does not support file uploads.
3. Always use the sender block to identify form submitters.
4. Handle errors gracefully. Check for error in the response.
5. Use E.164 format for phone numbers (e.g., +12025550123).
6. Use ISO 3166-1 alpha-2 codes for countries (e.g., US, GB, TR).

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Resources

• Form Blocks Reference
• File Uploads Guide
• API Reference