Creating your first node

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, and an html file that defines the node’s properties, edit dialog and help text.

When packaged as an npm module, they also include a package.json file that pulls it all together.

To begin creating your own node, you can either create it as a simple ‘local’ node or go straight to packaging it as a proper module.

Creating a simple node

A local node just consists of the .js and .html files.

These files can be located within either the nodes directory in your user directory, typically ~/.node-red/nodes, or one of the directories defined in the nodesDir setting.

The following example defines a simple node that converts a message payload into all lower-case characters.

lower-case.js

module.exports = function(RED) {
    function LowerCaseNode(config) {
        RED.nodes.createNode(this,config);
        var node = this;
        node.on('input', function(msg) {
            msg.payload = msg.payload.toLowerCase();
            node.send(msg);
        });
    }
    RED.nodes.registerType("lower-case",LowerCaseNode);
}

The node is wrapped as a node 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, RED, 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 initialise 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 npm installed alongside the node files.

lower-case.html

<script type="text/javascript">
    RED.nodes.registerType('lower-case',{
        category: 'function',
        color: '#a6bbcf',
        defaults: {
            name: {value:""}
        },
        inputs:1,
        outputs:1,
        icon: "file.png",
        label: function() {
            return this.name||"lower-case";
        }
    });
</script>

<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">
    </div>
</script>

<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>
</script>

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.