Aliases are nicknames for command calls and thus supersede a lot of typing. In Linux there exist the command alias, in Windows there is doskey. An alias can be defined as follows:

doskey ls=dir

Typed aliases are volatile , that means, these are no longer available after a recall of the command line console. In order to make them persistent two steps are necessary. Firstly, create a bat-script containing all aliases and save it to an arbitrary location. Secondly, insert a corresponding string value in the Windows registry.

1. Open Registry by searching „regedit“
2. Open HKEY_CURRENT_USER → SOFTWARE → Microsoft → Command Processor
3. Add new String Value called AutoRun with the path to the created bat-script.

Whenever a command line console is opened, the script is loaded and automatically executed in the current session.

Webpack is a newer module bundler continuously gaining popularity. It can be basically viewed as a replacement for grunt or gulp. Webpack has a broad feature set: It can be used to bundle AMD, CommonJS and ES2015 modules. Further, it provides a feature known as code splitting that allows to group the code in multiple bundles in order to optimize how it is downloaded. Moreover, webpack can be used to bundle javascript, css, images and other assets. It also provides loaders that can be used to preprocess files before bundling them. In this blog post, I’m going to scratch the surface of loaders. I like to demonstrate how to configure the babel-loader with webpack in order that the files are transpiled whenever webpack is called.

First of all, we need to install webpack in the project as well as globally using npm.

Next, we need to install the babel-loader as well as the babel-core. These are 3rd party components provided by babel. If babel-cli and babel-preset-es2015 in not yet installed, install them as well.

Next, we have to configure the webpack.config.js which contains the configuration for webpack. It is basically a CommonJS module.

The input file is assumed to be app.js placed in the folder js. The transpiled and bundled file will be located in the folder build and is called bundle.js. Without going into the details, the loader will look for all files ending with .js  exluding the files in the node_modules. Then, it will manipulate the files and turn them from es6 to es5. To make all this happen, we only need start a command line in the project and type in webpack.

There are a lot more useful loaders that can be configured. For example, there exist a css-loader which bundles all css files, a saas-loader that does the same for saas files and a url-loader that can be used to bundle images and fonts. Without further explanation, they are inserted below.

The overall goal of Spring Boot devtools is to improve the development time. It’s available since Spring Boot version 1.3 and it includes different features among others property default, live reload, automatic restart etc.

Spring Boot devtools works by watching the classpath for any build changes and then automatically restarts the application. In Eclipse or most other IDE, every time you save, it actually builds the code. In IntelliJ, however, the code is not every time fully built when it is saved or automatically saved. In this short post, I like to demonstrate how you can configure automatic restart with IntelliJ.

First of all, you need to add devtools to your dependencies. Note that the dependency is optional in order that it is not transitively included in other projects.

Next, we record a macro by selecting Edit → Macros → Start Macro Recording. Thereafter the following two steps must be recorded:

1. File → Save All
2. Build → Make Project

Once this is done, you can stop the recording via Edit → Macros → Stop Macro Recording and give a name, e.g. „Spring Boot Automatic Restart“ to the recorded macro. Next, go to keymap in the settings (File → Settings ). Copy the current keymap and rename it to „Spring Boot Keymap“ for example. Scroll down to macros and select your recorded macro. Via the context menu (right-click) add a keyboard shortcut like CTRL + S.

Whenever your Spring Boot application is running and CTRL + S is pressed, an automatic restart is done. Spring Boot devtools works with two classloaders. One that loads all the classes in the beginning and another one that only loads the changes. Thus, a startup improvement can be achieved. I observed on my machine, that the startup time is more than halved by using devtools and its automatic restart.

Given the following ArrayList containing a couple of items having a name and a value:

Let’s assume we want to group the items by name and sum up all values. With the aid of Java 8, we can do it as follows:

In order to get an ArrayList again, we can iterate over the map, create new items from each entry and add this to a list:

I was wondering how to do the same calculation using JavaScript as there is no similar goupingBy function. And here it is… We need to implement the groupingBy functionality by using the reduce function.

The this keyword is one of the most misunderstood and confusing aspect in JavaScript. This has a completely different meaning in JavaScript than in most other programming languages. Because programmers try to apply the meaning of other programming languages to JavaScript, this often results in great confusion. To understand this, however, you have to put aside all known concepts from other programming languages. This in Javascript has nothing to do with classes or their instantiation or similar concepts from other programming languages.

Every function, while executing, has a reference to its current execution context, called this.

In JavaScript, this is a reference to its current execution context, i.e. this is given by the call site (location in code where the function is called).  What this means exactly, is further discussed below.

Let me give a first example:

If you are not in strict mode default the this keyword to the global object. Since the variable is cash in the global object is this.bar equal „bar“. However, if you are in strict mode, to Uncaught TypeError: Can not read property ‚bar‘ of undefined is thrown. In strict mode, this is the undefined value.

Above The example has been extended with an Object o1. If the o1.foo () method is called the current execution context is to o1. Thus „bar2“ output. This is called implicit binding.

call, apply, bind
bind: use it if you want to be predictable
############ EXAMPLE ############

new
############ EXAMPLE ############
Kyle Simpsons summarizes these facts in his book „You don’t know Javascript“ under 4 rules in order of precednece:

4 rules in order of precedence to never be again confues about the this keyword:

was the function called with new?
was the function called with call or apply specifing an excplicit this?
was the function called via a conaining/owning object(context)?
default: global object (except strict mode)

ECMAScript 6 hat arrow Funktionen eingeführt. Dort verhält sich this nochmals ein wenig spezieller wie folgendes Beispiel zeigt:

arrow functions: we get the context where the code is running
you can not bind a new object to an arrow function. the javascript does even throw an error, it just ignores the bind. call, bind and apply are all useless when using arrow functions. You can not change the this context when using arrwo functions.