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Start publishing with JavaScript

Create a Node.js™ client that publishes data through topics on the Diffusion™ server.

To complete this example, you need a Diffusion server and a development system with Node.js and npm installed on it.

You also require either a named user that has a role with the modify_topic and update_topic permissions. For example, the "ADMINISTRATOR" role. For more information about roles and permissions, see Role-based authorization.

This example steps through the lines of code required to publish to a topic. There are several different topic types which provide data in different formats. This example shows you how to publish to a JSON topic. The full code example is provided after the steps.
  1. Install the Diffusion JavaScript® library on your development system. 
    npm install --save diffusion
  2. Create the JavaScript file that will be your publishing client.
    For example, publishing.js
    1. Require the Diffusion library. 
      const diffusion = require('diffusion');
    2. Connect to the Diffusion server. 
      diffusion.connect({
                host : 'host-name',
                principal : 'control-user',
                credentials : 'password'
                }).then(function(session) {
                console.log('Connected!');
                });

      Where host-name is the name of the system that hosts your Diffusion server, control-user is the name of a user with the permissions required to create and update topics, and password is the user's password.

    3. Create a JSON topic called foo/counter. 
      session.topics.add("foo/counter", diffusion.topics.TopicType.JSON);
    4. Every second update the value of the topic with the value of the counter. 
          setInterval(function() {
                session.topics.update('foo/counter', { count : i++ });
                }, 1000);
  3. Use Node.js to run your publishing client from the command line. 
    node publishing.js
The publisher updates the value of the foo/counter topic every second. You can watch the topic value being updated by subscribing to the topic.
The completed publishing.js file contains the following code: 
const diffusion = require('diffusion');
        
        diffusion.connect({
        host : 'hostname',
        principal : 'control-user',
        credentials : 'password'
        }).then(function(session) {
        console.log('Connected!');
        
        var i = 0;
        
        // Create a JSON topic
        session.topics.add("foo/counter", diffusion.topics.TopicType.JSON);
        
        // Start updating the topic every second
        setInterval(function() {
    
        session.topics.update("foo/counter", { count : i++ });

        }, 1000);
        
        });
Now that you have the outline of a publisher, you can use it to publish your own data instead of a counter.

This page last modified: 2017/07/20