
Today I ran into the problem of trying three objects, evenly spaced on the screen of a mobile device. But that brought more trouble than I initially thought. It's a pretty common scenario. In my case, it was for a podcast view and trying to fit a title, a poster image, and the controls above the fold. It could also be a landing page where you want to fit an interesting title, a blurp, and a call to action button on the first screen that the users see.

![Example](/images/vertically-center-content-with-css/example.png)

We know that we want the content centered on the page and that we need some space in between. It sounds like a job for Flex!

```html
<div class="screen">
  <div class="centered-content">
     <div class="centered-content__item">
       <h1>
         Make up to $35 Driving Your Car
       </h1>
     </div>
      <div class="centered-content__item">
       <p>
         How many ours do you want to drive per week?
       </p>
     </div>
      <div class="centered-content__item">
       <button>
         Become a Driver
       </button>
     </div>
  </div>
</div>

```

```css
.screen {
  height: 100vh;
  width: 100%;
}

.centered-content {
  align-items: center;
  display: flex;
  flex-direction: column;
  height: 100%;
  justify-content: center;
  text-align: center;
  width: 100%;
}

.centered-content__item {
  margin-bottom: 128px;
}

```

So let's break this down:

- First, we create a container that will cover the whole screen.
- Inside the container, we use Flex to center the content.
- We add a margin to the bottom of each item so that they have some room to breathe.

Pretty good so far. 🎉

But when we try it on a smaller screen, the content won't fit. Because of the fixed margin, the content will take up the same amount of space on any screen and that becomes a problem here.

<div class="flex flex-wrap justify-center">
  <img alt="Margin on iPhone XL" class="block shadow-lg" src="/images/vertically-center-content-with-css/i-phone-xl-margin.png" />
  <img alt="Margin on iPhone 5" class="block shadow-lg" src="/images/vertically-center-content-with-css/i-phone-5-margin.png" />
</div>

One approach to this would be to use Media Queries. That way, we can conditionally format the content depending on the screen height. I would like to avoid that. Even though Media Queries gives you a lot of control, it also adds extra complexity to our stylesheets.

So thinking a bit more about the spacing, we want it dynamically adjust depending on the space available. We can use `justify-content: space-between` which spreads the items out evenly.

```css
.centered-content {
  align-items: center;
  display: flex;
  flex-direction: column;
  height: 100%;
  justify-content: space-between;
  text-align: center;
  width: 100%;
}

```

This works a lot better on our small device. But now there is way too much space between the items on a bigger screen.

<div class="flex flex-wrap justify-center">
  <img alt="Space Between on iPhone XL" class="block shadow-lg" src="/images/vertically-center-content-with-css/i-phone-xl-justify.png" />
  <img alt="Space Between on iPhone 5" class="block shadow-lg" src="/images/vertically-center-content-with-css/i-phone-5-justify.png" />
</div>

In situations like this, when we have conflicting behavior, it's because we want to do too many things. We need to cut boards and punch nails and we are trying to get our hammer to do both. The good thing about programming is that we can create new tools!  We can add a new class that spaces the content out.

```css
.centered-content {
  align-items: center;
  display: flex;
  flex-direction: column;
  height: 100%;
  justify-content: center;
  text-align: center;
}

.centered-content__evenly-spaced {
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  height: 100%;
  max-height: 620px;
}

```

This way, we have a whole new class that's only responsible for handling the spacing of the items. The interesting addition here is that it will fill the whole screen on smaller screens.

But as the screen grows in height, the `max-height` property will limit how big it can get to avoid spacing things out too much.

<div class="flex flex-wrap justify-center">
  <img alt="Max Height on iPhone XL" class="block shadow-lg" src="/images/vertically-center-content-with-css/i-phone-xl-max-height.png" />
  <img alt="Max Height on iPhone 5" class="block shadow-lg" src="/images/vertically-center-content-with-css/i-phone-5-max-height.png" />
</div>

```html
<div class="screen">
  <div class="centered-content">
    <div class="centered-content__evenly-spaced">

     <div>
       <h1>
         Make up to $35 Driving Your Car
       </h1>
     </div>

      <div>
       <p>
         How many ours do you want to drive per week?
       </p>
     </div>

      <div>
       <button>
         Become a Driver
       </button>
     </div>

    </div>
  </div>
</div>

```

```css
.screen {
  height: 100vh;
  width: 100%;
}

.centered-content {
  align-items: center;
  display: flex;
  flex-direction: column;
  height: 100%;
  justify-content: center;
  text-align: center;
}

.centered-content__evenly-spaced {
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  height: 100%;
  max-height: 620px;
}

```

<div class="flex flex-wrap justify-center">
  <img alt="Final Result on iPhone XL" class="block shadow-lg" src="/images/vertically-center-content-with-css/i-phone-xl-final.png" />
  <img alt="Final Result on iPhone 5" class="block shadow-lg" src="/images/vertically-center-content-with-css/i-phone-5-final.png" />
</div>

There is a lot of awesome tools we can use to create beautiful layouts but it still has a lot of challenges, especially in a world of a multitude of different screen sizes and devices.

Focusing on the different behaviors we want to accomplish is a good way to break things down. When things are getting too complex, try to keep each part simple and with their own responsibility.


Vertically Center Content with CSS on Mobile Devices


As our app consists of a couple of different bundles and a bunch of chunks, we noticed that our Cypress test suite was a bit flaky. Dynamically loading different Javascript and CSS files caused our test to fail due to timing issues.

Looking into a bit more we found that when we are calling `cy.visit()` to navigate to a page, we were ending up with tests that were randomly failing due to not all Javascript being loaded yet.

If you look at the documentation for `cy.visit` it says

> cy.visit() yields the window object after the page finishes loading.

While this is true, if you dig a bit deeper you'll realize that it yields on the window's on-load event. This will probably work well in most cases but as we are throttling our Javascript load we encounter some problems where not all the code that we need is downloaded when the on-load event is called.

Cypress has a `route` command that can be used to wait for and/or mock requests, but it only triggers on XHR request so it will do us no good as we are loading resources using link and script tags.

If you are curious about which request works with the `route` command you can use the `whitelist` property of `cy.server` to list them.

```js
cy.server({
  whitelist: request => {
     console.log(request);

     return false;
  };
});

cy.visit('/');
```

The Cypress team are working on a new network stubbing layer that will give us more control and granularity and that would probably make this task a lot easier but it still seems to be quite far away from being released.

If you are interested you can find out more in [Issue 687](https://github.com/cypress-io/cypress/issues/687).

It looks like we will have to build our own command, that will wait for resources to load. At first, it might be a bit unclear on how to track which resources are loaded via Javascript, at least it was for me. The idea of using a Service Worker to track the completion of requests and signal the app via `postMessage` was floated but seemed a bit too complicated.

We are in luck though, as the new Performance API has functions for measuring the loading time of different resources, and for us to be able to measure the time, the resource has to be loaded, right?

Using the `performance.getEntriesByType` function, we will end up with a list of already loaded resources, such as Javascript and CSS files.

If we continuously query the Performance API we'll know when a resource has been added to the list and we can continue on with our test case.

With a quick look at the Cypress documentation, we were are able to come up with a [custom command](https://docs.cypress.io/api/cypress-api/custom-commands.html) that waits for a resource to load.

```js
function waitForResourceToLoad(fileName, type) {
  const resourceCheckInterval = 40;

  return new Cypress.Promise(resolve => {
    const checkIfResourceHasBeenLoaded = () => {
      const resource = cy.state('window')
        .performance.getEntriesByType('resource')
        .filter(entry => !type || entry.initiatorType === type)
        .find(entry => entry.name.includes(fileName));

      if (resource) {
        resolve();

        return;
      }

      setTimeout(checkIfResourceHasBeenLoaded, resourceCheckInterval);
    };

    checkIfResourceHasBeenLoaded();
  });
}

Cypress.Commands.add('waitForResource', waitForResource);
```

We do a couple of things here that might be worth noting. First, we access the window object by using `cy.state`. This is due to the nature of the Cypress test runner. Using the global window object we will be operating on the test runners window, which won't have the data we need. By accessing it via `cy.state` we are able to get the applications window object, which lives within an iframe.

As well as a `fileName` of the resource we are waiting for, we also pass a `type` argument to the function. This is because when you are using Webpack's dynamic imports to load Javascript, it will use a link tag to preload the content and this will cause our Promise resolve once the script is preloaded and not when it's loaded.

Therefore, when we wait for dynamic imports we have to make sure we wait for the resource initiated by the script tag.

```js
cy.waitForResourceToLoad('dynamicly-loaded-bundle.js', 'script');
```

We can also use this command to wait for CSS files whose loading is deferred, to make sure that all our styles are applied before continuing.

```js
cy.visit('/');
cy.scrollTo(0, 500);

cy.waitForResourceToLoad('below-the-fold.css');
```

With this new command, we were able to replace a lot of arbitrary `cy.wait` commands from our tests, while making it more reliable.

I would love to know if you found this helpful and what kind of scenarios with dynamic resource loading you encountered writing Cypress tests for your application. Please leave a comment below. 😄


Waiting for network resources in Cypress


How do you build a countdown timer for your app that allows you to pause it and start it again, and design it in such a way it's easy to extend with different events in the future?

<p data-height="265" data-theme-id="light" data-slug-hash="qQqbOa" data-default-tab="result" data-user="Artmann" data-pen-title=" Countdown Timer" class="codepen">See the Pen <a href="https://codepen.io/Artmann/pen/qQqbOa/"> Countdown Timer</a> by Christoffer Artmann (<a href="https://codepen.io/Artmann">@Artmann</a>) on <a href="https://codepen.io">CodePen</a>.</p>
<script async src="https://static.codepen.io/assets/embed/ei.js"></script>

The simplest approach I can imagine is to save the time the user clicked the start button, then use `setInterval`  to continuously update the label.

```js
const duration = 10;
let startTime;

const label = document.querySelector('.time');

document.querySelector('button').addEventListener('click', () => {
    startTime = Date.now();

    setInterval(() => {
      const t = Math.ceil(duration - (Date.now() - startTime) / 1000);
      label.innerHTML = Math.max(0, t);
    }, 200);
});
```

This solution works well but if we want to expand on our timer like adding the ability to pause the countdown, for example, we will quickly see that this approach has a lot of limitations.

The other thing that bugs me about this approach is the use of `setInterval`. I used an arbitrary interval of 200 milliseconds here, and this value will always we a compromise.

 To increase the accuracy of our timer, we want that value to be as low as possible, setting it to zero would be awesome as it would be executed on the next run of the event loop. But as we lower the value we also negatively impact the performance of our page.

Fortunately for us, there is another function we can use and it's. **window.requestAnimationFrame**. As the name implies it's primary use is to give you a callback that you can use for animations. After calling `requstAnimationFrame` with a callback, the next time the browser wants to do a repaint it will run your callback before it continues to the repaint. This is perfect when we want to do to animations that feels really smooth at a higher framerate. The added bonus is that calls to `requestAnimationFrame` are paused in most browsers when running in background tabs or hidden Iframes in order to improve performance and battery life.

So now we have a better way to handle the timing, but we still need a more stable approach to keep track of the elapsed time. What we can do is that every time we run our function, we calculate the time since the last time we ran it. This is usually called the **Delta time**.  Then at every iteration, we aggregate the delta time with all the previous delta times.

```js
const elapsed = 0;
const lastTimestamp = 0;

const tick =  () => {
	const timestamp = Date.now();
	const deltaTime = timestamp - lastTimestamp;
	lastTimestamp = timestamp;

	elapsed += deltaTime / 1000;

	window.requestAnimationFrame(tick);
};

tick();
```

Now it's super easy for us to control if the timer should run or not.

```js
if (isActive) {
	elapsed += deltaTime / 1000;
}
```

We also have a good place to hook in when we want to update the DOM.

```js
const label = document.querySelector('.time');
const onTick = time => {
	label.innerHTML = Math.ceil(time);
}

...

if (isActive) {
	elapsed += deltaTime / 1000;
	const time = Math.max(duration - elapsed, 0);
	onTick(time);
}
```

Adding all the pieces together and encapsulating it in a class, it looks something like this.

<p data-height="265" data-theme-id="light" data-slug-hash="qQqbOa" data-default-tab="js" data-user="Artmann" data-pen-title=" Countdown Timer" class="codepen">See the Pen <a href="https://codepen.io/Artmann/pen/qQqbOa/"> Countdown Timer</a> by Christoffer Artmann (<a href="https://codepen.io/Artmann">@Artmann</a>) on <a href="https://codepen.io">CodePen</a>.</p>
<script async src="https://static.codepen.io/assets/embed/ei.js"></script>

If you have any questions or found this helpful, please leave a comment below! 😃 👋


Building a Javascript Countdown Timer


We recently decided to use [Tailwind CSS](https://tailwindcss.com/) for our
Ember app at work and it really struck a chord with me. That's why I decided to try it in Ruby on Rails.

As you are here you are probably already hyped to get started with Tailwind CSS in your Rails app but if
you still need convincing A wrote Adam Wathan about it, [CSS Utility Classes and "Separation of Concerns](https://adamwathan.me/css-utility-classes-and-separation-of-concerns/).

If you want to create a new app you can pass the `--webpack` option as of Rails 5.1

```shell
rails new myapp --webpack
```

Otherwise just add the *webpacker* gem.

```ruby
# Gemfile
gem 'webpacker', '~> 3.0'

bundle
bundle exec rails webpacker:install
```

Then install `autoprefixer` and `tailwindcss`

```shell
yarn add --dev autoprefixer tailwindcss
```

Webpacker lives in `app/javascript` as default. Lets create some new folders there to keep things organized and
create the default tailwind configuration file.

```shell
mkdir -p app/javascript/src app/javascript/styles

node_modules/.bin/tailwind init app/javascript/src/tailwind.js
```

Then we add the tailwind config to `application.css`. You can find it at <https://tailwindcss.com/docs/installation>

```css
# app/javascript/styles/application.css

@tailwind base;

@tailwind components;

@tailwind utilities;
```

Now we need to add our post css plugins to webpacker.

```yml
# .postcssrc.yml

plugins:
  postcss-import: {}
  postcss-cssnext: {}
  autoprefixer: {}
  tailwindcss: './app/javascript/src/tailwind.js'
```

And add our new folders to `resolved_paths` in `webpacker.yml`.

```yml
# config/webpacker.yml

resolved_paths: [
  'app/javascript/src',
  'app/javascript/styles'
]
```

Import the css file in webpackers entrypoint.

```js
// app/javascript/packs/application.js

import 'application.css';
```

And then link to the new files

```erb
# app/views/layouts/application.html.erb

<%= javascript_pack_tag 'application' %>
<%= stylesheet_pack_tag 'application' %>
```

## Heroku

If you are running your app on Heroku you'll have to adjust some settings to make it work with Webpacker and Tailwind.

First of, with later versions of Webpacker you'll have to add the Node buildpack and then the ruby one.

```shell
heroku buildpacks:clear
heroku buildpacks:set heroku/nodejs
heroku buildpacks:add heroku/ruby
```

Then you'll have to update the config var `YARN_PRODUCTION` to `false`.

That's it, folks. You can now use Tailwind CSS classes in your markup.

You can find a reference app at <https://github.com/artmann/rails-tailwind-example>


Adding Tailwind CSS to Your Rails App


When switching between languages I often find my self Googling on how to do string concatenation and especially interpolation which no two languages seems to agree on.

For future reference, Here's how you do it.

## C

In C, strings are really just plain `char` arrays. Therefore, you can't directly concatenate them with other strings.

You can use the `strcat` function, which appends the string pointed to by `src` to the end of the string pointed to by `dest`:

```c
char *strcat(char *dest, const char *src);
```

## C++

C++ has `std::string` which is used instead of `char` arrays.

```
string a = "Hello ";
string b = "World";
string c = a + b;
```

## C&#35;

C# lets you use the `+` operator to concatenate strings.

```cpp
string name = "Chris";
Console.WriteLine("Hello " + name);
```

It also allows for interpolation.

```
string firstName = "Sally";
string lastName = "Morgan";

Console.WriteLine($"Hello {firstName} {lastName}");
```

## Go

You can use the `+` operator to concatenate strings in Go.


```go
firtName := "James"
lastName := "Pierce"

fmt.Println(firstName + " " + lastName)
```

There's also `fmt.Sprintf` which lets you format strings.

```go
firtName := "Denise"
lastName := "Richards"

fullName = fmt.Sprintf("%s %s", firstName, lastName)
```

Strings are read-only in Go so a new object is generated every time you concatenate two strings. If this becomes a problem you can use `bytes.buffer`.

```go
var buffer bytes.Buffer

buffer.WriteString("Hello")
buffer.WriteString(" ")
buffer.WriteString("World")

fmt.Println(buffer.String())
```

## Java

Java also uses the `+` operator to concatenate strings.

```java
String name = "Molly";

System.out.println("Hello " + name);
```

## Javascript

Javascript uses the `+` operator to concatenate strings.

```js
let firstName = 'Isabela';
let lastName = 'Wang';

console.log(firstName + ' ' + lastName);
```

You can also interpolate strings with backticks.

```js
let firstName = 'Megan';
let lastName = 'Fox';

console.log(`Hello ${firstName} ${lastName}`);
```

## PHP

PHP uses `.` to concatenate strings.

```php
$firstName = 'Lisa';
$lastName = 'Swan';

echo $firstname . ' ' . $lastName;
```

Only variables can be interpolated.

```php
$name = 'Michelle';

echo "Hello {$name}";
```

## Ruby

Ruby uses the `+` operator to concatenate strings.

```ruby
fist_name = 'Tyler'
last_name = 'Reed'

puts fist_name + ' ' + last_name
```

And it uses `#{}` for interpolation

```ruby
name = 'Sarah'

puts "Hello #{name}"
```

## Python

Python uses the `+` operator to concatenate strings.

```python
firstName = "Emma"
lastName = "Stone"

print(firstName + " " + lastName)
```

And from version 3.6 you can interpolate strings.

```python
name = "Sally"

print(f"Hello {name}")
```


String Concatenation Cheat Sheet


```js
// trucks/controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  trucks: [{name: 'truck 1', inUse: false}, {name: 'truck 2', inUse: true}],

  actions: {
    changeTruck(truck, inUse) {
      Ember.set(truck, 'inUse', inUse);
    }
  }
});
```
```
// ddau-checkbox/component.js

import Ember from 'ember';

export default Ember.Component.extend({
  tagName: 'input',
  attributeBindings: ['checked', 'type'],
  type: 'checkbox',
  change() {
    if (this.attrs['on-change']) {
      let checked = this.$().is(':checked');
      this.attrs['on-change'](checked);
    }
   }
});
```
```
// trucks/template.hbs
{{#each trucks as |truck|}}
  <table>
    <tbody>
      <tr>
        <td>{{truck.name}}</td>
        <td>
          {{ddau-checkbox checked=truck.inUse on-change=(action 'changeTruck' truck)}}
        </td>
      </tr>
    </tbody>
  </table>
{{/each}}
```


Curry actions from DDAU Checbox component


Allowing your users to upload images to your application is not an unusual feature but I had to pull some of my hair before I found an approach I liked when trying to do it with Ember.

At first we need a component for the file-input as there is no built-in view for this yet.

```js
App.InputFileComponent = Ember.Component.extend({
  attributeBindings: ['multiple', 'type'],
  tagName: 'input',
  type: 'file',
  multiple: true,
  files: null,
});
```

Then can use it in our template like this

```js
{{input-file files=files}}
```

And files is the property we are going to use to store our files.
Then we want something to happen when the user chooses which files to upload. We can do this by listening to the change event and populate our array with the files uploaded

```js
change: function(event) {
  var files = event.target.files;
  for (var i = 0; i < files.length; i++) {
    var file = files.item(i);
    this.get('files').pushObject(file);
  }
}
```

We can now render our files on the page.

```js
<ul>
{{#each file in files}}
  {{file.name}}
{{/each}}
</ul>

{{input-file files=files}}
```

But displaying just the filename is a bit boring, is it not? As luck would have it, thanks to components it won’t be too hard to show a preview of the image next to the name. If we remove the list item from our template and replace it with a component. We can do something like this.

```js
<ul>
{{#each file in files}}
  {{image-preview file=file}}
{{/each}}
</ul>
{{input-file files=files}}
```

By creating a image preview component we can use the FileReader class to read our image data and bind it to a img-tag

```js
App.ImagePreviewComponent = Ember.Component.extend({
  tagName: 'li',
  file: null,

   didInsertElement: function () {
     var self = this;
     var file = this.get('file');
     var reader = new FileReader();
     reader.onload = function(e) {
       var data = e.target.result;
       self.$("img.preview").attr("src", data);
     };
     reader.readAsDataURL(file);
   },
});
```


Image uploads with Ember.js


Apache vs Nginx. Passenger vs Unicorn vs Puma. I’ve personally been running Apache with Passenger as I got a lot more of Apache experience then with Nginx but when setting up the servers for a recent Rails project I was not really happy about the number of requests I could serve.

The test site is running on Digital Ocean $10 servers which yield the following specs

* 1GB Memory
* 1 CPU Core
* SSD Drives

I use one server for the database, one with Apache + Passenger and one with Nginx + Puma. Then I used another server with some more power behind it to run Apache Benchmark with a conccurency level between 10 and 500.

I bashed the servers with 200, 1000, 5000, 10000 requests to measure number of request per seconds it could handle and the mean response time.

## Requests per second

![request per secod](http://i.imgur.com/Z6V8S1O.jpg)

## Mean response time

![Mean response time](http://i.imgur.com/Z6V8S1O.jpg)

So it seems when it comes to Passenger vs Puma it seems like Puma  is the way to go.



## Open source is great

The value of open source development has reached even greater spread and hopefully this will lead to additional exchange of knowledge.

## Love your ecosystems

Having a community around your product and then most importantly, have a product which allows your community to extend and modify it for their own personal needs.

## Big data will get even bigger

Big data has been the thing to talk about for a while now and it’s still growing and recent analysis shows that by 2020 the amount of storage needed will be around 40 exabytes, that would equal about 85 million years of HD video.
Seagate presented that they needed to innovate and move away from their classical disk manufacturing and the current way of building SANs. When they presented their new Kinetic disks they showed that they really have started to innovate and are building disks for object storage that can communicate over Ethernet.

## Detach your resources

We have been moving our storage out from our servers for quit a while now and Intel presented that they want to do the same with the rest of our system resources. Using fiber optics they want to move memory and CPU out of the servers and into a rack level.

## Arm enters the data center

AMD was present to talk about their new investment into Arm processor wanting to create CPUs for specific tasks like video rendering and data analytics.

## Microsoft impresses

With their new concept, Cloud OS which is based on Windows server and Azure pack among others and lets you build and move between public and private clouds and alot of other cool features.

## Learn to love your orchestration layer

While automated deployment and provisioning continue to grow and PaaS and SaaS are getting more popular the demand for on-demand infrastructure will increase.

## Focus on the things you are good at and do them better

Identify the parts of your business that you do the best, focus on these and partner up with top actors in your edge areas.



Vertically Center Content with CSS on Mobile Devices

Waiting for network resources in Cypress

Building a Javascript Countdown Timer

Adding Tailwind CSS to Your Rails App

String Concatenation Cheat Sheet

Curry actions from DDAU Checbox component

Image uploads with Ember.js

Image uploads with Ember.js

My impressions from World Hosting Days 2014

Hi, I'm Chris!