Creating your first node

Using Docker/Terminal creating your node

Written By Brian Sathinathan (Super Administrator)

Updated at January 5th, 2021

Nodes get created when a flow is deployed, they may send and receive some messages whilst the flow is running and they get deleted when the next flow is deployed.

They consist of a pair of files:

  • a JavaScript file that defines what the node does,
  • an html file that defines the node’s properties, edit dialog and help text.

package.json file is used to package it all together as an npm module.

Creating a simple node

This example will show how to create a node that converts message payloads to all lower-case characters.

Ensure you have the current LTS version of Node.js installed on your system. At the time of writing this is 10.x.

Create a directory where you will develop your code. Within that directory, create the following files:

  • package.json
  • lower-case.js
  • lower-case.html


This is a standard file used by Node.js modules to describe their contents.

To generate a standard.package.json file you can use the command.npm initThis will ask a series of questions to help create the initial content for the file, using sensible defaults where it can. When prompted, give it the name node-red-contrib-example-lower-case.

Once generated, you must added a node-red section:

    "name" : "node-red-contrib-example-lower-case",
    "node-red" : {
        "nodes": {
            "lower-case": "lower-case.js"

This tells the runtime what node files the module contains.

For more information about how to package your node, including requirements on naming and other properties that should be set before publishing your node, refer to the packaging guide.

Note: Please do not publish this example node to npm!


module.exports = function(RED) {
    function LowerCaseNode(config) {
        var node = this;
        node.on('input', function(msg) {
            msg.payload = msg.payload.toLowerCase();

The node is wrapped as a Node.js module. The module exports a function that gets called when the runtime loads the node on start-up. The function is called with a single argument, that provides the module access to the Node-RED runtime api.


The node itself is defined by a function, LowerCaseNode that gets called whenever a new instance of the node is created. It is passed an object containing the node-specific properties set in the flow editor.

The function calls the RED.nodes.createNode function to initialize the features shared by all nodes. After that, the node-specific code lives.

In this instance, the node registers a listener to the input event which gets called whenever a message arrives at the node. Within this listener, it changes the payload to lower case, then calls the send function to pass the message on in the flow.

Finally, the LowerCaseNode function is registered with the runtime using the name for the node, lower-case.

If the node has any external module dependencies, they must be included in the dependencies section of its package.json file.

For more information about the runtime part of the node, see here.


<script type="text/javascript">
        category: 'function',
        color: '#a6bbcf',
        defaults: {
            name: {value:""}
        icon: "file.png",
        label: function() {

<script type="text/x-red" data-template-name="lower-case">
    <div class="form-row">
        <label for="node-input-name"><i class="icon-tag"></i> Name</label>
        <input type="text" id="node-input-name" placeholder="Name">

<script type="text/x-red" data-help-name="lower-case">
    <p>A simple node that converts the message payloads into all lower-case characters</p>

A node’s HTML file provides the following things:

  • the main node definition that is registered with the editor
  • the edit template
  • the help text

In this example, the node has a single editable property, name. Whilst not required, there is a widely used convention to this property to help distinguish between multiple instances of a node in a single flow.

For more information about the editor part of the node, see here.

Testing your node in Node-RED

Once you have created a basic node module as described above, you can install it into your Node-RED runtime.

To test a node module locally the npm install <folder> command can be used. This allows you to develop the node in a local directory and have it linked into a local node-red install during development.

In your node-red user directory, typically ~/.node-red, run:

npm install <location of node module>

For example, on Mac OS or Linux, if your node is located at ~/dev/node-red-contrib-example-lower-case you would do the following:

cd ~/.node-red
npm install ~/dev/node-red-contrib-example-lower-case

On Windows you would do:

cd C:\Users\my_name\.node_red
npm install C:\Users\my_name\Documents\GitHub\node-red-contrib-example-lower-case

This creates a symbolic link to your node module project directory in ~/.node-red/node_modules so that Node-RED will discover the node when it starts. Any changes to the node’s file can be picked up by simply restarting Node-RED. On Windows, again, using npm 5.x or greater:Notenpm will automatically add an entry for your module in the package.json file located in your user directory. If you don’t want it to do this, use the --no-save option to the npm install command.

Unit Testing

To support unit testing, an npm module called node-red-node-test-helper can be used. The test-helper is a framework built on the Node-RED runtime to make it easier to test nodes.

Using this framework, you can create test flows, and then assert that your node properties and output is working as expected. For example, to add a unit test to the lower-case node you can add a test folder to your node module package containing a file called _spec.js


var should = require("should");
var helper = require("node-red-test-helper");
var lowerNode = require("../lower-case.js");

describe('lower-case Node', function () {

  afterEach(function () {

  it('should be loaded', function (done) {
    var flow = [{ id: "n1", type: "lower-case", name: "test name" }];
    helper.load(lowerNode, flow, function () {
      var n1 = helper.getNode("n1");'name', 'test name');

  it('should make payload lower case', function (done) {
    var flow = [{ id: "n1", type: "lower-case", name: "test name",wires:[["n2"]] },
    { id: "n2", type: "helper" }];
    helper.load(lowerNode, flow, function () {
      var n2 = helper.getNode("n2");
      var n1 = helper.getNode("n1");
      n2.on("input", function (msg) {'payload', 'uppercase');
      n1.receive({ payload: "UpperCase" });

These tests check to see that the node is loaded into the runtime correctly, and that it correctly changes the payload to lower case as expected.

Both tests load the node into the runtime using helper.load supplying the node under test and a test flow The first checks that the node in the runtime has the correct name property. The second test uses a helper node to check that the output from the node is, in fact, lower case.

The helper module contains other examples of tests taken from the Node-RED core nodes. For more information on the helper module, see the associated README.

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