Node.js server for offline export of Plotly.js graphs

This repository contains a Node.js application that starts a server which can render Plotly.js graphs to SVG images without sending the data to the servers of Plotly. That means all plot data stays on this local server and is NOT sent over the net. If you value the privacy of your data, this might be a better option for you than using the API on the Plotly servers.

Requirements

This application needs one prerequisite:

• Node.js 18 or later (preferably the latest LTS version)

Installation of Node.js

The installation of Node.js is covered in a separate document.

(If you prefer a setup within a Docker container over a native installation, then please take a look at Setup with Docker.)

Initial setup: install Node.js dependency packages

The application requires a package for jsdom. To install that, type

npm install

in the directory export-server/. You only need to do this once. The packages are then cached in the node_modules/ directory for future use.

Start the application

You can simply start the application via

npm start

which fires up the Node.js application. The server will then listen on http://localhost:3000/ for incoming connections.

If you want the server to listen on a different port, then you can set the environment variable PORT accordingly. On Linux-like systems you can do

export PORT=4000
npm start

The equivalent on Windows command prompt would be

SET PORT=4000
npm start

In these cases the server will bind to port 4000 instead of the default port 3000.

The hostname can be changed, too, by setting the HOST environment variable in the same manner, e. g.:

export HOST=0.0.0.0
npm start

If HOST is not set, then localhost will be used as hostname.

Usage

To generate a SVG file of a Plotly plot, just send an HTTP POST request to the running Node.js server on http://localhost:3000/ containing the data for the plot as JSON in its body.

For example, POSTing the following JSON code to the server

{
  "x": ["2013-10-04 22:23:00", "2013-11-04 22:23:00", "2013-12-04 22:23:00"],
  "y": [1, 3, 6],
  "type": "scatter"
}

will generate a SVG image that looks like this:

The generated image will be contained in the response message body.

Adjusting the width and height of the generated image

The generated SVG image has a width of 700 pixels and a height of 400 pixels by default. If no size is specified, then the image will be of that default size. However, this may not always be suitable for your needs.

To change the size, add the HTTP headers X-Image-Width and / or X-Image-Height to the request. Acceptable values are integers only, the values will be interpreted as pixels, not centimetres, inches or other. For example, if you want the image to be 750 x 500 pixels, then set the HTTP headers

X-Image-Width: 750
X-Image-Height: 500

Using the same JSON as above, the created image will now be slightly larger and look like this:

Troubleshooting

If you encounter problems while trying to generate a plot image, then please take a look at the FAQ. Some common errors and possible solutions are listed there.

Version history

A version history is available in changelog.md.

Copyright and Licensing

Copyright 2018, 2020, 2021, 2022, 2023, 2024 Dirk Stolle

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.