Tutorial by Examples: s

Spawning a process to run an executable

If you are looking to run a file, such as an executable, use child_process.execFile. Instead of spawning a shell like child_process.exec would, it will directly create a new process, which is slightly more efficient than running a command. The function can be used like so: const execFile = require(...

Node.js • Executing files or commands with Child Processes

Testing Exceptions

Programs throw errors when for instance wrong input is given. Because of this, one needs to make sure that an error is thrown when actual wrong input is given. Because of that we need to check for an exact exception, for this example we will use the following exception: class WrongInputException(Ex...

Python Language • Unit Testing

Using ManyToMany Fields

We use this model from the first example: class Person(models.Model): name = models.CharField(max_length=50) description = models.TextField() class Club(models.Model): name = models.CharField(max_length=50) members = models.ManyToManyField(Person) Add Tom and Bill to the N...

Django • Many-to-many relationships

Repeat an action x times

repeat(10) { i -> println("This line will be printed 10 times") println("We are on the ${i + 1}. loop iteration") }

Kotlin • Loops in Kotlin

Looping over iterables

You can loop over any iterable by using the standard for-loop: val list = listOf("Hello", "World", "!") for(str in list) { print(str) } Lots of things in Kotlin are iterable, like number ranges: for(i in 0..9) { print(i) } If you need an index while...

Kotlin • Loops in Kotlin

While Loops

While and do-while loops work like they do in other languages: while(condition) { doSomething() } do { doSomething() } while (condition) In the do-while loop, the condition block has access to values and variables declared in the loop body.

Kotlin • Loops in Kotlin

Strategy

A strategy pattern can be used in Javascript in many cases to replace a switch statement. It is especially helpful when the number of conditions is dynamic or very large. It allows the code for each condition to be independent and separately testable. Strategy object is simple an object with multip...

JavaScript • Conditions

Using Elements from the Polymer Catalog

Polymer prodives a lot of well built elements for you to use in your app. Browse them in their Element Catalog. Let's go through the workflow of using an element by including paper-input (Documentation) Download the Element To Download an element there are two ways: Bower The convinient way is...

polymer • Getting started with polymer

Basic Element Structure

We got the following very basic element my-element saved as src/my-element.html <link rel="import" href="bower_components/polymer/polymer.html"> <dom-module id="my-element"> <template> <style> /* local styles go here */ ...

polymer • Getting started with polymer

Example showcasing the basic concepts

The following example is an introduction to: Template compilation using underscore Accessing variables in a template Creating a view Rendering a view Showing a view <html> <head> <script src="https://code.jquery.com/jquery-3.1.0.min.js"></script> ...

backbone.js • Getting started with backbone.js

Generic algorithms

Higher-order functions can be used to implement generic algorithms, giving up the responsibility of providing final details to the user. For instance List.sort expects a comparison function, which allows to implement various ways of sorting. Here we implement case-insensitive sorting of strings: le...

OCaml • Higher Order Functions

Dispose system resources even when an exception is raised

Higher-order functions can be used to ensure that system resources are disposed, even when a treatment raises an exception. The pattern used by with_output_file allows a clean separation of concerns: the higher-order with_output_file functions takes care of managing the system resources bound to fi...

OCaml • Higher Order Functions

List.Map

List.map has the signature ('a -> 'b) -> 'a list -> 'b list which in English is a function that takes a function (we'll call this the mapping function) from one type (namely 'a) to another type (namely 'b) and a list of the first type. The function returns a list of the second type where ev...

OCaml • List Processing

File/Directory details

The ls command has several options that can be used together to show more information. Details/Rights The l option shows the file permissions, size, and last modified date. So if the root directory contained a dir called test and a file someFile the command: user@linux-computer:~$ ls -l Would ...

GNU/Linux • Getting started with GNU/Linux

Changing default shell

Most modern distributions will come with BASH (Bourne Again SHell) pre-installed and configured as a default shell. The command (actually an executable binary, an ELF) that is responsible for changing shells in Linux is chsh (change shell). We can first check which shells are already installed and...

GNU/Linux • Shell

Hot and Cold Observables

Observables are broadly categorised as Hot or Cold, depending on their emission behaviour. A Cold Observable is one which starts emitting upon request(subscription), whereas a Hot Observable is one that emits regardless of subscriptions. Cold Observable /* Demonstration of a Cold Observable */ Ob...

rx-java • Observable

Set CSS property

Setting only one style: $('#target-element').css('color', '#000000'); Setting multiple styles at the same time: $('#target-element').css({ 'color': '#000000', 'font-size': '12pt', 'float': 'left', });

jQuery • CSS Manipulation

Get CSS property

To get an element's CSS property you can use the .css(propertyName) method: var color = $('#element').css('color'); var fontSize = $('#element').css('font-size');

jQuery • CSS Manipulation

Unit testing using Theories

From JavaDoc The Theories runner allows to test a certain functionality against a subset of an infinite set of data points. Running theories import org.junit.experimental.theories.Theories; import org.junit.experimental.theories.Theory; import org.junit.runner.RunWith; @RunWith(Theories...

junit • Tests

Creating basic deadlocked system

A deadlock occurs when two competing actions wait for the other to finish, and thus neither ever does. In java there is one lock associated with each object. To avoid concurrent modification done by multiple threads on single object we can use synchronized keyword, but everything comes at a cost....

Java Language • Concurrent Programming (Threads)