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How to use Parallel to speed up building the same html partial multiple times (for different data)

The parallel-gem is quite easy to use and can speed up rendering time if you want to render the same partial multiple times (e.g. for rendering long lists of things).
If your parallelized code talks to the database, you should ensure not to leak database connections.

Consider you want to render a list of groups with their members as json. You can use a partial for the rendering of group members, b...

How to: Throttle CPU in Google Chrome

Chrome allows you to throttle the Network and the CPU. Both settings are useful to measure the performance of you application and reproduce performance issues (Example Debugging frontend performance issues with Chrome DevTools).

You find the settings in: DevTools > Performance > Capture Settings (Gear icon in the right corner) > `CPU: No...

Repeats

Always disable autocomplete for date pickers

When we write a form with date fields, we often use graphical data picker like Rome to get a consistent calendar popup on all browsers.

When you integrate a date picker popup, remember to also set autocomplete="off" on the text input that opens the calendar on click. Otherwise the autocomplete suggestions will cover the calendar box and make it unusable:

Image

If you are using a tool like Unpoly you might want to set autocomplete="off" i...

Repeats

Cucumber's table diffing does not play nice with Spreewald's `patiently do`

Turns out, Cucumber::MultilineArgument::DataTable#diff! caches some stuff. Code of the following form will not work as intended:

Then('some table should look like') do |expected_table|
  patiently do
    actual_table = calculate_actual_table
    expected_table.diff!(actual_table) # not actually patient, will keep failing if it failed the first time
  end
end

Instead, simply use

expected_table.dup.diff!(actual_table)
Repeats

How to use a local gem in your Gemfile

You can use local copies of gems in your Gemfile like this:

gem 'spreewald', :path => '~/gems/spreewald'

As soon as you have bundled your project with the local copy of the gem, all code changes in the copy will be available on your project. So you can for example set a debugger or add console output in the gem and use it from your project.
If you checked out the gem with your versioning tool, you can easily reset your changes afterwards or make a pull request for the gem if you improved it.

Don't commit a Gemfile with local pat...

Repeats

How to simulate limited bandwidth in Google Chrome and Firefox

Your development machine is usually on a very good network connection.
To test how your application behaves on a slow network (e.g. mobile), you can simulate limited bandwidth.

Chrome

  • Open the dev tools (Ctrl+Shift+I or F12) and switch to the "Network" tab
  • In the row below the dev tool tabs, there's a throttling dropdown which reads "Online" by default.
  • Inside the dropdown, you will find a few presets and an option to add your own download/upload/latency settings.

Firefox

  • Open the dev tools (Ctrl+Shift+I or F12) and switc...
Linked contentRepeats

Printing background color of elements

Browsers' printing methods usually don't print background colors. In most cases this is the desired behavior, because you don't want to spent tons of ink printing the background of a web page. But in some cases you want to print the background color of elements, e.g. bars of a chart. For those elements you need to set the following css styles:

-webkit-print-color-adjust: exact; /* Chrome and Safari */
color-adjust: exact; /* Firefox */

Note that if you're using autoprefixer, you don't need...

Video transcoding: Web and native playback overview (April 2020)

Intro

Embedding videos on a website is very easy, add a <video> tag to your source code and it just works. Most of the time.

The thing is: Both the operating system and Browser of your client must support the container and codecs of your video. To ensure playback on every device, you have to transcode your videos to one or more versions of which they are supported by every device out there.

In this card, I'll explore the available audio and video standards we have right now. The goal is to built a pipeline that transcodes unknown ...

Linked contentRepeats

Colorful output for several linux command line tools: grc

Because colors improve readability so much.
On Ubuntu 18.04 you can install it with sudo apt install grc

From github:

For the impatient - try following commands:

grc netstat
grc ping hostname
grc tail /var/log/syslog
grc ps aux
Linked contentRepeats

Beware: Many browsers define window.event

Some browsers define window.event, which will return a copy of the "current" event. However, this is not defined by the W3C. Most importantly, Firefox does not support it, neither do recent versions of IE.

You should completely avoid accessing the global event and instead pass the event object around that the event handler receives. The easiest protection against accidentally accessing window.event is just never naming the event event, but e or evnt or so.

function brokenInFirefox() {
  event.preventDefault(); // Break...
Repeats

Operators "in" and "of" are very inconsistent between CoffeeScript and JavaScript

CoffeeScript and JavaScript (ECMAScript) both have operators in and of. Each language use them for more than one purpose. There is not a single case where the same operator can be used for the same purpose in both languages.

Check if an object (or its prototype) has a property

CoffeeScript

var hasFoo = 'foo' of object

JavaScript

var hasFoo = 'foo' in object;

Iterate through all properties of an object
================================...

Repeats

Checklist: Rails Authentication

Authentication is a special part of web applications. On the one hand, it usually is a crucial security mechanism restrict access to certain people and roles. On the other hand, most users authenticate only once, so it is very unlikely to spot issues by accident.

So, here comes a quick checklist to help you verifying your authentication solution is all set.

  • This should be default: use HTTPS with HSTS. The HSTS part is important.
  • Use a reliable authentication solution, e.g. Clearance or [Devise...

Devise: How to allow only HTTP Basic Auth and disable the HTML sign-in form

By default, Devise redirects to a sign-in form when accessing a route that requires authentication. If for some reason you do not want this, but use Basic Authentication (and the corresponding browser username/password dialog) instead, this is a simple change.

Note that Devise's default configuration actually only redirects requests for HTML content (as requested by the HTTP Accept header).
For all other formats (like JSON) it would use Basic Auth if the http_authenticatable setting was enabled. So you can simply enable that flag and cl...

How to write good code comments

Code comments allow for adding human readable text right next to the code: notes for other developers, and for your future self.

As always, with great power comes great responsibility. Code comments can go wrong in many ways: they may become outdated, silently move away from the code they're referring to, restate the obvious, or just clutter files.

Good Comments

Here are some simple rules to keep your comments helpful:

Avoid stating what some code does – prefer the Why

Some say, perfect code would not need a single comment. Th...

Repeats

Popular mistakes when using nested forms

Here are some popular mistakes when using nested forms:

  • You are using fields_for instead of form.fields_for.
  • You forgot to use accepts_nested_attributes in the containing model. Rails won't complain, but nothing will work. In particular, nested_form.object will be nil.
  • The :reject_if option lambda in your accepts_nested_attributes call is defined incorrectly. Raise the attributes hash given to your :reject_if lambda to see if it looks like you expect.
  • If you are nesting forms into nested forms, each model involved ne...
Repeats

Carrierwave: Deleting files outside of forms

TL;DR Use the #remove_<mounted_attribute>! method to delete attachments. Also, save the record after removing the file!


As you know, Carrierwave file attachments work by mounting an Uploader class to an attribute of the model. Though the database field holds the file name as string, calling the attribute will always return the uploader, no matter if a file is attached or not. (Side note: use #present? on the uploader to check if the file exists.)

class User < ApplicationRecord
  mount :avatar, AvatarUploader
end

...

Linked contentRepeats

Writing a README for a project

Rails applications and ruby gems should have a README that gives the reader a quick overview of the project. Its size will vary as projects differ in complexity, but there should always be some introductory prose for a developer to read when starting on it.

Purpose

That's already the main purpose of a project README: Give a new developer a quick overview of the project. In sketching this outline, the README should notify the reader of any peculiarity he needs to know of.

Remember that in a few months, you'll be a kind of "new ...

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