Node.JS demo program

Let's create some NODE.JS application that will communicate with active terminal and make it runnable from Linux bash shell...

Prerequisites

Install Node.JS
Create folder for your project and add file package.json
Open package.json with text editor and add minimum required, then save it
```
  {}
```
Position to project folder from console and execute following to install required lib
```
  npm install ws --save
  npm install mem-cache --save
```

Program

Create index.js in project folder and add code shown at the end of the page.

Code can be executed as bash shell script simply by calling ./index.js or with Node.JS itself by executing from command line with node index.js.

index.js file

#!/usr/bin/env node

const WebSocket = require('ws');
const Cache = require('mem-cache');

var cache = new Cache();
var ws = new WebSocket('ws://localhost:5250')

/**
 * Store request into cache and make remote request
 */
function request(req, callback) {

  // store request into cache for 30 seconds
  cache.set(req.rid, {callback : callback}, 30000);

  // send request to GreenScreens Native Terminal
  ws.send(JSON.stringify(req));
}

/**
 * Receive response from terminal and process data
 */
ws.on('message', function(resp, raw) {

   // parse received text data into JSON
   let data = JSON.parse(resp);

   // take rid from response and look into cache
   let cdata = cache.get(data.rid);

   // if request stored into cache and have callback function, execute it
   if (cdata && typeof cdata.callback === 'function') {
     cdata.callback(data);
   }
});

/**
 * Signal when connection established
 */
ws.on('open', function open() {

    // prepare A-HLL API command
    let req = {"cmd": "echo", "rid": Date.now()};

    // send A-HLL command to terminal and attach response handler
    request(req, function(resp){
      console.log(`Response arrived from terminal for request ID: ${resp.rid}`);
    });

});