Conventions

In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "ES2015 introduces the let keyword to declare variables that respect the block scope."

A block of code is set as follows:

const zmq = require('zmq')
const sink = zmq.socket('pull');
sink.bindSync("tcp://*:5001");

sink.on('message', buffer => {
  console.log(`Message from worker: ${buffer.toString()}`);
});

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

 function produce() {
   //...
   variationsStream(alphabet, maxLength)
     .on('data', combination => {
       //...
       const msg = {searchHash: searchHash, variations: batch};
       channel.sendToQueue('jobs_queue', 
new Buffer(JSON.stringify(msg)));
       //...
     })
   //...
 }

Any command-line input or output is written as follows:

node replier
node requestor

New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "To explain the problem, we will create a little web spider, a command-line application that takes in a web URL as the input and downloads its contents locally into a file."