each.js

const http = require("http"); //Package used to make http request
const async = require("async"); //Package used for async operation handling

//the callback that will  be used for async calling
//url - url passed to call the http server
//next - this will be a callback provided by async library so that we can call next function in async chain
const httpCallback = (url, next) => {
  http.get(url, res => {
    //Get method makes an http get request to the given url

    let httpResult = "";
    // on method sets up a 'data' event listner on the http response (as the response comes in chunks)

    res.on("data", chunk => {
      //concatenating the http response
      httpResult += chunk.toString();
    });
    //setting up clean up listeners for each event   (end -on the http response stream end, err - on http response stream error)
    res
      .on("end", () => {})
      .on("err", err => {
        //invokes the main callback with error object directly
        next(err);
      });
  });
};
//using async.each method that calls an async function on each element of array
async.each([process.argv[2], process.argv[3]], httpCallback, err => {
  //result of each callback is lost in case of async.each
  console.log(err);
});