Table of Contents for

Node.js 8 the Right Way

Developing a Node-RED Flow

When you develop a program in Node-RED, it’s called a flow. The Hello World of Node-RED flows consists of a button that, when clicked, outputs a timestamp to the debug console. We’ll start with this simple flow so you can get comfortable with the Node-RED interface before we move on to developing an HTTP API.

To begin, take a look at the left pane of the Node-RED interface. This shows the kinds of nodes you’ll use to construct flows, categorized by their purposes.

Input nodes act as sources of events into the system. You can tell an input node visually by the tiny gray rectangle protruding from its right-hand side. This gray rectangle is an output port.

If you hover over a node, a tooltip will pop up to give you more information about that node.

Click and drag an inject node from the left pane onto the flow pane. This will create an inject node in your flow (as shown in the figure).

Take a look at the node you just created. It will have an orange border to indicate that it’s the currently selected node, and a description of the node will appear in the Info tab of the right-side pane.

The node will also have a blue dot in its upper-right corner. This signals that the node has not yet been deployed.

When you make changes to a flow in the editor, these changes do not take effect immediately. To get them to take effect, you have to deploy your flow by clicking the red Deploy button.

There are three different deployment options, ranging from a full deploy down to just the changed nodes. In this chapter, we’ll always perform a full deploy.

If you haven’t done so already, click the Deploy button now. A Successfully deployed message should appear briefly at the top of the screen and the blue dot should disappear from your inject node.

When you deploy a flow, this is just like starting a server in regular Node.js code. It may not look like it’s doing anything, but it’s waiting for events to respond to.

Now, if you click the little square button protruding from the left side of the inject node, you should see the message Successfully injected: timestamp appear briefly (as shown in the figure).

When you click the Inject button, a Node-RED event is injected into the flow. Right now nothing is set up to receive that event, so let’s add a destination for it.

In the nodes pane on the left, scroll down to the output nodes. These nodes have input ports—little gray rectangles protruding from their left sides.

The first one in the list should be the debug node.

Click and drag a debug node onto the flow workspace, somewhere to the right of the inject node you added previously.

To connect the nodes, click and drag the output port of the inject node and join it to the debug node’s input port (or vice versa). You should see a curvy gray line appear between the nodes.

The debug node writes its output to the Debug tab of the right-side pane. Select that tab by clicking it, then deploy the flow.

Now when you click the inject node’s left-side button, you should see a JavaScript timestamp logged to the Debug tab.

The green button hanging off of the right-hand side of the debug node toggles whether it is active. Toggling it takes effect immediately (no need to redeploy). This is convenient during development because it allows you to leave the debug nodes in your flow without having them always log to the Debug tab.

When you double-click any node, this opens the node editor, allowing you to make changes to the node’s settings. Double-click the debug node now, then choose “complete msg object” from the drop-down for the Output setting (as shown in the figure).

Click the Done button to close the editor. Now when you click the Inject button, you’ll see the whole JSON object that it produced in the Debug tab.

And that’s it—you’ve made your first flow! Admittedly, this flow doesn’t do much—it waits for you to click the Inject button and then logs information to the Debug tab.

So let’s move on to something more intricate: using Node-RED to develop an HTTP API.