When I first heard about generators in the ES6 version of JavaScript, I wasn't quite sure how useful they would be. In this post I will look at the basics of generators in JavaScript and other languages. In a future post I'll explore how to combine Generators and Promises.

The following code uses generators to create a fibonacci sequence.

Today I am looking at Promises in JavaScript and how they are used to write easy to follow and error resistant asynchronous code. Before writing any Promises I made an async call in JavaScript the traditional way; with callbacks. I didn't use any fancy JavaScript framework to make my async http request, just the simple XMLHttpRequest object (which is as poorly named as AJAX - it can be used for much more than XML!)¹.

I made a custom google search API which was really easy and fun to create²! It searches certain websites for cat related posts (and is appropriately called meowmeow)! Who wouldn't love that? In my code I retrieve the article names from the top 10 searches in my custom meow search. The code uses the XMLHttpRequest object and a callback function:

In many programming languages arrow functions are added to allow for concise one liners and decreased verbosity. Less lines of code is one of the things that made the Java 8 release with lambdas so appealing. In ES6 JavaScript also added arrow functions to write shorter, more readable code. However, in JavaScript the arrow functions aren't as universally praised due to some quirks.

In JavaScript I looked at this and how its set dynamically at runtime instead of depending on its lexical scope. I also went over how many JavaScript users (including myself!) are easily confused by how this works. Arrow functions look to 'fix' these confusions by implementing a lexical this. Now the value of this in an arrow function depends on what this was equal to when arrow function was written (instead of when its called). This leads to confusing behavior if you are expecting arrow functions to act like normal function definitions. Let's look at an example.

One JavaScript feature I've used before but never fully understood is strict mode. Strict mode restricts certain features and leniencies in the language¹. It protects the developer from things that happen implicitly in JavaScript (that only an experienced dev would be aware of). In a previous discovery I looked at how strict mode disallows this from containing the global scope variable. What else does strict mode have to offer?

Certain things that silently fail in JavaScript throw errors when executed in strict mode. This includes setting properties to primitives and assigning values to keywords.

In this discovery I look at sorting lists in different programming languages for non-trivial objects. The languages I use are my core languages: Java, JavaScript, Swift, Python, PHP, and C. I've used all these languages in larger projects and wish to stay proficient in them. Throughout this article I show snippets of code in each language, but you can also check out the full code on GitHub. Let's get started!

Java

When you run code in JavaScript there is a global object created in the global scope. What this object is depends on the environment JavaScript is running in. If you run JavaScript code in your web browser the global object is window, which represents the browser window. Window exposes an API for interaction with the Document Object Model (DOM), click listeners, and other information about the browser window¹.

In the past I have used the window object to check the current URL and previous page visited by the user (to create a 'back' button). However, the most common use of window is to manipulate the DOM and set click listeners (I used frameworks such as JQuery to perform these tasks in the past).

In my last discovery post on graph databases and Neo4j, I created a graph representing a map of Fairfield County, Connecticut. I created nodes for all the towns/cities and edges between the settlements that shared borders. This discovery adds to the graph and shows some of the challenges I faced along the way. Let's dive in!

First I populated the graph with some people (after all, a settlement needs citizens!).

this in JavaScript is part of the language that always confused me. The keyword doesn't work like its Java counterpart where it refers to the object instance of a method or constructor. Often in the past when using this I took shortcuts such as the popular var self = this statement so I wouldn't worry about the value of this in nested functions.

What makes this so confusing is that it's set at runtime instead of author time (compile time)¹. In other words it doesn't follow the rules of lexical scope that I am comfortable with. this is incredibly daunting for new programmers since its value can be different when calling the same function on separate occasions.

In my last discovery post, I went over the revealing module pattern in JavaScript. Now I am recreating the same API with ES6 modules. The API code will look familiar:

The only change to the API is the export keyword. export is a new keyword in ES6 that reveals the function lyrics to other JavaScript code. Any JavaScript file can be a module if it exports functions/variables. Only one module can exist per file, and each module can export multiple items. Since one file is one and only one module, the name of a module is the filename. Code to import a module uses the import keyword:

In JavaScript there are multiple module patterns for creating APIs and separating concerns in code (as of ES6 there is also official module syntax in the spec). In the following code I created an API using the revealing module pattern. The name 'revealing module pattern' comes from the return statement at the end of the module - it 'reveals' functions to outside code.

This module provides lyrics for Taylor Swift songs (because who doesn't enjoy some T-Swift!) The return statement is the public API for the module. All interior details, such as the lyric variable, are hidden. This pattern harnesses the power of closure in JavaScript!

JavaScript has quickly become one of the languages I use the most (probably second behind Java). Many people use JavaScript along with one of its many frontend frameworks (JQuery, AngularJS, etc.) without really knowing how the core language operates. I don't want to be one of those people!

This is my first of many discovery posts on JavaScript. Let's look at one of the basic concepts of the language: how variables interact with scope. Scope describes the area of a program where a variable is accessible (e.g. a variable declared in a function is only accessible within that function). Scope is also the execution environment for each line of a program. It consists of the variables and functions a program line is aware of. In JavaScript, scope can get a bit tricky.

Lately I've read about graph databases and their place in the NoSQL data storage universe. The graph database I've worked with is Neo4j, which is fun and easy to get started with. I found the user interface very enjoyable for viewing graphs and executing queries. I highly recommend it if you need a graph database solution.

Graph databases largest draw is related data storage and the speed at which you can query related data points (or in graph terms, nodes/vertices). Relationships are first class citizens, which allows related data queries to be executed by traversing relationships themselves. This is contrasted with a typical relational database where you have to find relationships through foreign keys or combine two tables with a very slow SQL JOIN operation¹. The same slow query in a RDBMS (Relational DataBase Management System) is extremely quick in a graph database.