polotno-node

Polotno-node

Export Polotno JSON into images and pdf files. NodeJS package to work with Polotno SDK.

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Usage

npm install polotno-node

const fs = require('fs');
const { createInstance } = require('polotno-node');

async function run() {
  // create working instance
  const instance = await createInstance({
    // this is a demo key just for that project
    // (!) please don't use it in your projects
    // to create your own API key please go here: https://polotno.dev/cabinet
    key: 'nFA5H9elEytDyPyvKL7T',
  });

  // load sample json
  const json = JSON.parse(fs.readFileSync('polotno.json'));

  const imageBase64 = await instance.jsonToImageBase64(json);
  fs.writeFileSync('out.png', imageBase64, 'base64');

  // close instance
  instance.close();
}

run();

API

createInstance(options)

Create working instance of Polotno Node.

const { createInstance } = require('polotno-node');
const instance = await createInstance({
  // this is a demo key just for that project
  // (!) please don't use it in your projects
  // to create your own API key please go here: https://polotno.dev/cabinet
  key: 'nFA5H9elEytDyPyvKL7T',
  // useParallelPages - use parallel pages to speed up rendering
  // you can use false only for sequential calls
  // it may break rendering if you call many parallel requests
  // default is true
  useParallelPages: false,
  // url - url of the Polotno Client Editor
  // client editor is just simple public html page that have `store` as global variable
  // by default it will run local build
  url: 'https://yourappdomain.com/client',
  // browser - puppeteer browser instance
  // by default it will use chrome-aws-lambda
  // useful to set your own rendering props or use browserless
  browser: browser,

  // browserArgs - additional browser arguments to append to default args
  // see "Custom Browser Arguments" section for more details
  browserArgs: ['--custom-arg'],

  // requestInterceptor - optional function to intercept and modify network requests
  // Useful when you need to:
  // - Modify headers like User-Agent to access protected image resources
  // - Add authentication tokens or credentials to requests
  // - Log or monitor network traffic
  requestInterceptor: (request) => {
    const targetUrl = request.url();
    if (/\.(png|jpe?g)(\?|$)/i.test(targetUrl)) {
      console.log(`Modifying User-Agent for image request: ${targetUrl}`);
      request.continue({
        headers: {
          ...request.headers(),
          'User-Agent': 'MyCustomApprovedAgent/1.0',
        },
      });
    } else {
      request.continue();
    }
  },
});

createBrowser(options)

Create a Puppeteer browser instance with optimized settings for Polotno rendering. This is useful when you want to create a browser separately from the instance.

const { createBrowser, createInstance } = require('polotno-node');

// Create a browser
const browser = await createBrowser({
  browserArgs: ['--custom-arg'], // optional: additional browser arguments
  // ... any other puppeteer.launch options
});

// Create instance with the browser
const instance = await createInstance({
  key: 'your-key',
  browser: browser,
});

Note: createBrowser() automatically uses the optimized args for rendering. You can add custom arguments via the browserArgs parameter.

instance.jsonToDataURL(json, attrs)

Export json into data URL.

const json = JSON.parse(fs.readFileSync('polotno.json'));

// by default it will export first page only
const url = await instance.jsonToDataURL(json);
res.json({ url });

// export many pages:
for (const page of json.pages) {
  const url = await instance.jsonToDataURL(
    { ...json, pages: [page] }, // for optimization, we can modify JSON to include only one page
    { pageId: page.id }
  );
  // do something with url
}

instance.jsonToImageBase64(json, attrs)

Export json into base64 string of image.

const json = JSON.parse(fs.readFileSync('polotno.json'));

// by default it will export first page only
const imageBase64 = await instance.jsonToImageBase64(json, {
  mimeType: 'image/png',
}); // also 'image/jpeg' is supported
fs.writeFileSync('out.png', imageBase64, 'base64');

// export many pages:
for (const page of json.pages) {
  const imageBase64 = await instance.jsonToImageBase64(
    { ...json, pages: [page] }, // for optimization, we can modify JSON to include only one page
    { pageId: page.id }
  );
  // do something with base64
}

instance.jsonToPDFBase64(json, attrs)

Export json into base64 string of pdf file.

const json = JSON.parse(fs.readFileSync('polotno.json'));

// it will export all pages in the JSON
const pdfBase64 = await instance.jsonToPDFBase64(json);
fs.writeFileSync('out.pdf', pdfBase64, 'base64');

instance.jsonToPDFDataURL(json, attrs)

Export json into data url of pdf file.

const json = JSON.parse(fs.readFileSync('polotno.json'));

const url = await instance.jsonToPDFDataURL(json);
res.json({ url });

instance.jsonToGIFDataURL(json, attrs)

Export json into data url of GIF file with animations

const json = JSON.parse(fs.readFileSync('polotno.json'));

const url = await instance.jsonToGIFDataURL(json);
res.json({ url });

instance.jsonToGIFBase64(json, attrs)

Export json into data url of GIF file with animations

const json = JSON.parse(fs.readFileSync('polotno.json'));

const base64 = await instance.jsonToGIFBase64(json);
fs.writeFileSync('out.gif', base64, 'base64');

attrs usage

NOTE: all export API will pass attrs object into relevant export function from store.

const url = await instance.jsonToDataURL(json, { pixelRatio: 0.2 });
// under the hood it will call:
// const url = await store.toDataURL({ pixelRatio: 0.2 });

attrs.assetLoadTimeout

You can add assetLoadTimeout attribute to attrs object. It will be used to set timeout for loading assets. By default it is 30000ms.

const url = await instance.jsonToPDFDataURL(json, { assetLoadTimeout: 60000 });

attrs.fontLoadTimeout

Timeout for loading fonts. By default it is 6000ms.

const url = await instance.jsonToPDFDataURL(json, { fontLoadTimeout: 10000 });

attrs.htmlTextRenderEnabled

Enabled experimental HTML text rendering. By default it is false.

const url = await instance.jsonToPDFDataURL(json, {
  htmlTextRenderEnabled: true,
});

attrs.textVerticalResizeEnabled

Enabled vertical text resize and align. By default it is false.

const url = await instance.jsonToPDFDataURL(json, {
  textVerticalResizeEnabled: true,
});

attrs.skipFontError

If skipFontError is true, it will not throw error font is not loaded or not defined. By default it is false, so it will throw error.

const url = await instance.jsonToPDFDataURL(json, {
  skipFontError: true,
});

attrs.skipImageError

If skipImageError is true, it will not throw error an can't be loaded. By default it is false, so it will throw error.

const url = await instance.jsonToPDFDataURL(json, {
  skipImageError: true,
});

attrs.textOverflow

Control behavior of text on its overflow. Default is change-font-size. It means it will automatically reduce font size to fit text into the box. Other options are:

• resize (change text element height to make text fit)
• ellipsis (add ellipsis to the end of the text)

const url = await instance.jsonToPDFDataURL(json, {
  textOverflow: 'resize',
});

attrs.textSplitAllowed

Additinal options to overflow behaviour. Default is false. It means the render will make sure no words are rendered into several lines. If you set it to true, the render will split words into several lines if needed without reducing font size.

const url = await instance.jsonToPDFDataURL(json, {
  textSplitAllowed: true,
});

instance.run()

Run any Polotno store API directly inside web-page context.

Warning: by default every run and every export function will create a new page with its own editor and context. If you want to make and export after you use instance.run() you must do it inside the same run function.

// we can't directly use "json" variable inside the run function
// we MUST pass it as the second argument
const url = await instance.run(async (json) => {
  // you can use global "config" object that has some functions from "polotno/config" module
  window.config.addGlobalFont({
    name: 'MyCustomFont',
    url: 'https://example.com/font.otf',
  });

  // you can use global "store" object
  store.loadJSON(json);
  await store.waitLoading();
  return store.toDataURL();
}, json);

window.config usage

window.config is a global object that has some functions from polotno/config module. You can use it to add custom fonts and customize some settings. Not all options are supported yet. If you see anything missing, please create an issue. You can see all available options in client.js file.

You should be able to change config before you call store.loadJSON function and do you export.

const url = await instance.run(async (json) => {
  // you can use global "config" object that has some functions from "polotno/config" module
  window.config.unstable_setTextVerticalResizeEnabled(true);
  // you can use global "store" object
  store.loadJSON(json);
  return store.toDataURL();
}, json);

Custom Browser Arguments

Using args export

polotno-node exports a carefully curated set of Chrome arguments (args) that are optimized for server-side rendering. These arguments are automatically used when you call createInstance() without providing your own browser.

const { args } = require('polotno-node');

console.log(args);
// Will show the default arguments like:
// ['--disable-web-security', '--allow-file-access-from-files', '--disable-gpu', ...]

Using with custom browser

When you want to use your own browser instance (e.g., with browserless.io or custom puppeteer configuration), you can still use these default arguments:

const { createInstance, args } = require('polotno-node');
const puppeteer = require('puppeteer-core');

// Use polotno-node's default args with your custom browser
const browser = await puppeteer.launch({
  args: args,
  headless: true,
  // ... other browser options
});

const instance = await createInstance({
  key: 'your-key',
  browser,
});

Modifying default arguments

If you need to add or remove specific arguments, you can do so by spreading the array:

const { createInstance, args } = require('polotno-node');
const puppeteer = require('puppeteer-core');

// Add custom arguments
const browser = await puppeteer.launch({
  args: [...args, '--custom-arg', '--another-custom-arg'],
});

// Remove specific arguments
const filteredArgs = args.filter((arg) => arg !== '--disable-gpu');
const browser2 = await puppeteer.launch({
  args: filteredArgs,
});

// Replace specific arguments
const customArgs = args.map((arg) =>
  arg === '--disable-web-security' ? '--enable-web-security' : arg
);
const browser3 = await puppeteer.launch({
  args: customArgs,
});

Combining with browserArgs option

When using createInstance() or createBrowser(), you can provide additional arguments via browserArgs option. These will be appended to the default arguments:

const { createInstance } = require('polotno-node');

const instance = await createInstance({
  key: 'your-key',
  browserArgs: ['--custom-arg', '--another-arg'],
});

Your own client

By default polotno-node ships with the default Polotno Editor with its (hopefully) last version. If you use experimental API such as unstable_registerShapeModel and unstable_registerShapeComponent, the rendering may fail if you use unknown elements types.

In that case you can use your own client editor. You need to create a public html page with store as global variable and mount just <Workspace /> component from polotno/canvas module. Take a look into client.html file and client.js file in this repo as a demo. In your own version of the Editor you can use experimental API to define custom components.

Pass url option to createInstance function with public url of your client editor.

**Note: you will have to maintain the last version of your client editor by yourself. Better to keep using the last **

const { createInstance } = require('polotno-node');

const instance = await createInstance({
  key: 'KEY',
  url: 'https://yourappdomain.com/client',
});

Usage on the cloud

AWS Lambda

polotno-node works with AWS Lambda out of the box. Here's a simple example:

const { createInstance } = require('polotno-node');

export const handler = async (event) => {
  const instance = await createInstance({
    key: process.env.POLOTNO_API_KEY,
  });

  const base64 = await instance.jsonToImageBase64(event.json);

  await instance.close();

  return {
    statusCode: 200,
    headers: {
      'Content-Type': 'image/png',
    },
    body: base64,
  };
};

Important: For reliable performance, you may need to increase AWS Lambda limits:

• Memory: Increase from the default. For complex designs, you may need to set it to maximum.
• Timeout: Increase from the default. For large files, you may need to set it to maximum.
• Ephemeral Storage: May need to increase from the default for complex designs.

Without these increases, polotno-node may work on smaller files but will fail or timeout on larger files.

Full working example: See polotno-node-aws-lambda for a complete demo.

AWS Lambda with Layers (Optional)

For advanced usage, you can use Lambda Layers to manage dependencies like chromium separately. This can help with deployment size and organization.

Dependencies:

• @sparticuz/chromium
• puppeteer-core
• polotno-node

Requirements:

• The chromium and puppeteer versions need to be compatible. Please check this document.
• The Memory limit needs to be increased from the default. You may need to set it to maximum for complex designs.
• The timeout should be increased from the default. You may need to set it to maximum for large files.

Creating a Lambda Layer with chromium:

• Create a .zip file from a chromium project:

mkdir chromium-112 && cd chromium-112

npm init -y
npm install @sparticuz/chromium@112.0

zip -r chromium.zip ./*

• Go to AWS console then open Lambda section and click on Layers.
• Following the documentation create a Layer with a chromium dependency by uploading a zip file. Keep in mind that environment like nodejs18.x should match between layer and function.

The size of the zip will be large, so you may need to use S3 to upload it.

• Finally, open the Lambda function, select a Code section, at the bottom click on Add Layer and select a created layer.

Handler code with custom chromium:

Create index.mjs:

import chromium from '@sparticuz/chromium';
import puppeteer from 'puppeteer-core';
import { createInstance, args } from 'polotno-node';

export const handler = async (event) => {
  const browser = await puppeteer.launch({
    // Combine chromium args with polotno-node's optimized args
    args: [...chromium.args, ...args],
    defaultViewport: chromium.defaultViewport,
    executablePath: await chromium.executablePath(),
    headless: true,
    ignoreHTTPSErrors: true,
  });

  const polotnoInstance = await createInstance({
    key: process.env.POLOTNO_API_KEY,
    browser,
  });

  const body = await polotnoInstance.jsonToImageBase64(event.json);

  await polotnoInstance.close();

  return {
    statusCode: 200,
    headers: {
      'Content-Type': 'image/png',
    },
    body,
  };
};

AWS Lambda fonts issue

Lambda functions do not include any fonts by default. If you encounter Timeout for loading font <font name> errors, you need to provide basic fonts (Arial and Times or their analogs).

Solution: Add fonts to your Lambda function

• Create a fonts folder in the root of your handler project.

mkdir fonts

• Put the Arial.ttf and Times.ttf files into the fonts folder. You can get them from your system fonts folder.

• Usage of fonts analogues is also possible:

  • If you don't want to use system Arial and Times fonts, you can use Liberation Fonts as free alternative. Download fonts from repository. Put LiberationMono-Regular.ttf and LiberationSans-Regular.ttf inside fonts folder.
  • Create file fonts.conf inside fonts folder. It should contain the following lines:

  <?xml version="1.0"?>
  <!DOCTYPE fontconfig SYSTEM "fonts.dtd">
  <fontconfig>
  <alias>
    <family>Arial</family>
    <prefer>
      <family>Liberation Sans</family>
    </prefer>
  </alias>
  <alias>
    <family>Times New Roman</family>
    <prefer>
      <family>Liberation Serif</family>
    </prefer>
  </alias>
  
  <dir>/var/task/fonts</dir>
  </fontconfig>
  

• Upload your Lambda function as usual, fonts will be loaded automatically.

AWS EC2

EC2 has some troubles with loading fonts. To fix the issue install Google Chrome, it will load all required libraries.

curl https://intoli.com/install-google-chrome.sh | bash

Got it from here: https://github.com/puppeteer/puppeteer/issues/765#issuecomment-353694116

Browserless usage

You can speed up your function execution a lot, if instead of using full browser you will use browserless.io service. It is a paid service not affiliated with Polotno.

Using browserless.io you can also make your function much smaller in size, so it will be possible to deploy to cloud provider with smaller limits, like Vercel.

// (!) loading from polotno-node/instance will not import puppeteer and chromium-min dependencies
const { createInstance } = require('polotno-node/instance');
const puppeteer = require('puppeteer');

const instance = await createInstance({
  key: 'nFA5H9elEytDyPyvKL7T',
  browser: await puppeteer.connect({
    browserWSEndpoint: 'wss://chrome.browserless.io?token=API_KEY',
  }),
  url: 'https://yourappdomain.com/client', // see "Your own client" section
});

Minimal usage

Also you can use @sparticuz/chromium-min to reduce function size. Make sure it is caching chromium binary in your cloud provider. Looks like Vercel is NOT doing that!

npm install @sparticuz/chromium-min

const { createInstance } = require('polotno-node/instance');
// Import args from main entry point for optimal browser configuration
const { args } = require('polotno-node');
const chromium = require('@sparticuz/chromium-min');
const puppeteer = require('puppeteer-core');

const makeInstance = async () => {
  const browser = await puppeteer.launch({
    // Combine chromium args with polotno-node's optimized args
    args: [...chromium.args, ...args],
    defaultViewport: chromium.defaultViewport,
    executablePath: await chromium.executablePath(
      'https://github.com/Sparticuz/chromium/releases/download/v110.0.1/chromium-v110.0.1-pack.tar'
    ),
    headless: chromium.headless,
    ignoreHTTPSErrors: true,
  });

  return await createInstance({
    key: 'your-key',
    browser,
  });
};

const instance = await makeInstance();

Troubleshooting

If you have an error like this

Unhandled Promise Rejection {"errorType":"Runtime.UnhandledPromiseRejection","errorMessage":"Error: Evaluation failed: ReferenceError: store is not defined\n at **puppeteer_evaluation_script**:3:9"

It may mean that Polotno Client Editor was not loaded in puppeteer instance. It is possible that you are missing required files in node_modules folder. I got this error when I was trying to run polotno-node on Vercel. To fix the issue you need to add this config into vercel.json:

{
  "functions": {
    "api/render.js": {
      // remember to replace this line with your function name
      "includeFiles": "node_modules/polotno-node/**"
    }
  }
}

Changelog

[2.12.30] - 2025-10-20

• Added args export, optimize args passed into the browser
• Remove --disable-font-subpixel-positioning from default args