It is very common to parse dates from strings. It seems obvious to use Date.parse for this job. However this method does not validate the input and tries to guess the format of the string.

This can lead to a very unexpected results:

Date.parse('Foobar_09_2018')
# Tue, 09 Oct 2018

In most of the cases it would be better to use Date.strptime as you can provide a date or time pattern to match against.

Date.strptime('Foobar_09_2018', '%d_%m_%Y')
# ArgumentError (invalid strptime format - `%d_%m_%Y')

Date.strptime('01_09...

This page lists many query methods and options in ActiveRecord which do not sanitize raw SQL arguments and are not intended to be called with unsafe user input. Careless use of these methods can open up code to SQL Injection exploits. The examples here do not include SQL injection from known CVEs and are not vulnerabilites themselves, only potential misuses of the methods.

Please use this list as a guide of what not to do.

You are given two CSS selectors that you do not control. How can you build a new selector that matches both of them?

item_selector = 'div'
active_selector = '.is-active'

Can't I just concat these selectors?

# Bad
new_selector = "#{item_selector}#{active_selector}"
# => "div.is-active"

Don't! This will break as soon as one of the selectors is actually a selector list.

item_selector = 'div, span, p' # <- Selector list 
new_selector # => "div, span, p.is-active" (wrong)

Solution

Wrap both selectors ...

Reacting on a class getting added can be done with a mutation observer. Example:

const items = document.querySelectorAll('.item')
const expectedClass = 'active'
const activeObserver = new MutationObserver((mutations) => {
  mutations.forEach((mutation) => {
    if (mutation.target.classList.contains(expectedClass) {
      // Do something
    }
  })
})
items.forEach(item => activeObserver.observe(item, { attributes: true, attributeFilter: ['class'] }))

Note that this is not a generic solution – it makes a few assumptions to simplif...

The Visual Viewport API enables developers to access the actually visible area of the page. This differs from the normal viewport if:

• the user has pinch-zoomed
• the on-screen keyboard is visible
• there are other page-independent artifacts

Obtain a VisualViewport from window.visualViewport. The object has the properties offsetLeft and offsetTop, and three events: resize, scroll, scrollend. You can use these to place and keep an element within the visual vi...

Added that usage of * wildcards might be necessary in custom fingerprinting rules.

Starting Terminator with split screens is quite simple: Just store a layout and start Terminator with the --layout <your layout> option.

However, if you want to run custom commands in your terminals, you need to do some work to keep these terminals from closing after a command exits. You accomplish this by tweaking bash to run a command before actually starting.

Pimp your .bashrc

Add this to the end of .bashrc:

# hack to keep a bash open when starting it with a command
[[ $startup_cmd ]] && { declare +x $startup_cmd; hi...

Checking if a JavaScript value is of a given type can be very confusing:

• There are two operators typeof and instanceof which work very differently.
• JavaScript has some primitive types, like string literals, that are not objects (as opposed to Ruby, where every value is an object).
• Some values are sometimes a primitive value (e.g. "foo") and sometimes an object (new String("foo")) and each form requires different checks
• There are three different types for null (null, undefined and NaN) and each has different rules for...

When dealing with time zones in Rails, there is one key fact to keep in mind:

Rails has configurable time zones, while
Ruby is always in the server's time zone

Thus, using Ruby's time API will give you wrong results for different time zones.

"Without" time zones

You can not actually disable time zones, because their existence is a fact. You can, however, tell Rails the only single time zone you'll need is the server's.

config.time_zone = "Berlin" # Local time zone
config.active_record.default_timezone = :loca...

• Updated card title
• Added a section about controlling issue grouping in the Sentry UI (i.e. without modifying the application)

Added a reference to a similar behavior when chrome is deliberately slowing down the setInterval and setTimeout rate

Sometimes you want to write a test for a business rule that's based on multiple variables. In your goal to cover the rule thoroughly, you start writing tests for each permutation of all variables. Quickly it blows up into something unsustainable. With n variables for the business rule, you get 2n permutations/test cases. This is manageable with 2 variables (4 test cases), but at 3 variables (8 test cases) it becomes ridiculous, and anything beyond that feels immediately uncomfortable.

I've noticed myself using an alternate pattern for...

I recently stumbled over a quirk in the way Ruby handles local variables that I find somewhat dangerous.

Consider:

def salutation(first_name, last_name = nil)
  if last_name
    full_name = "#{first_name} #{last_name}"
  end 
  "Hi #{full_name}"
end 

This is obviously wrong, full_name is unset when last_name is nil.

However, Ruby will not raise an exception. Instead, full_name will simply be nil, and salutation('Bob') returns 'Hi '.

The same would happen in an else branch:

def salutation(fi...

Sometimes we have to write code that behaves differently based on the version of a specific gem or the Ruby Version itself. The version comparison can often be seen with simple string comparison like so.

# ❌ Not recommended
if Rails.version > '6.1.7.8' || RUBY_VERSION > '3.1.4'
  raise Error, 'please check if the monkey patch below is still needed'
end

If you are lucky, the version comparison above works by coincidence. But chances are that you are not: For example, Rails version 6.1.10.8 would not raise an error in the code ...

Further relaxed the requirements for implementation. Once all scenarios/examples are written down, the order of test-writing and implementation does not actually matter.

Rails gives you migrations to change your database schema with simple commands like add_column or update.
Unfortunately these commands are simply not expressive enough to handle complex cases.

This card outlines three different techniques you can use to describe nontrivial migrations in Rails / ActiveRecord.

Note that the techniques below should serve you well for tables with many thousand rows. Once your database tables grows to millions of rows, migration performance becomes an iss...

The tree command will show you the contents of a directory and all its sub directories as a tree:

>tree
.
├── a
│   ├── file_1.txt
│   └── file_2.txt
└── b
    ├── c
    │   └── even_more.txt
    └── more.txt

3 directories, 4 files

If you have deeply nested directories, the output will be quite long though. To avoid that, you can limit the depth, e.g. tree -L 2 will only go 2 directories deep.

If you use that regularly, consider adding aliases for that to your ~/.bashrc:

alias tree2='tree -L 2'
alias tree3='tree -L 3'
...

When you're nesting setTimeout(f, 0) calls, your browser will silently increase the delay to 5 milliseconds after the fourth level of nesting.

This is called "timeout clamping" and defined in the HTML spec:

If nesting level is greater than 5, and timeout is less than 4, then set timeout to 4.

Timeouts are clamped harder in background tabs

On a similar note, all major browsers have implemented throttling rules for setInterval and setTimeout calls from tabs...

I was recently asked to optimize the response time of a notoriously slow JSON API endpoint that was backed by a Rails application.
While every existing app will have different performance bottlenecks and optimizing them is a rabbit hole of arbitrary depth, I'd like to demonstrate a few techniques which could help reaching actual improvements.

The baseline

The data flow examined in this card are based on an example barebone rails app, which can be used to reproduce the r...

tl;dr

To adjust code templates in RubyMine, navigate to Settings -> Editor -> File and Code Templates.

Example

You can navigate to the test file of the currently open file with the shortcut Ctrl + T. If no test file exists, you can generate a new test file. If you are not pleased with the output, you can adjust the related code template. To do this, open the project settings and navigate to Editor -> File and Code Templates -> Files. Now, choose your relevant file type and adjust the code template according ...

Unpoly enhances your HTML with new attributes to build dynamic UI on the server. It works with any language and gracefully degrades without JavaScript.

The 3.9.0 release brings many fixes and quality-of-life improvements that were requested by the community. The vast majority of these changes are backward compatible. One breaking change can be found with making links followable. Existing usage is polyfilled by [`unpoly-migr...

In Ruby, the meaning of protected and private is different from other languages like Java. (They don't hide methods from inheriting classes.)

private

Private methods can only be called with implicit receiver. As soon as you specify a receiver, let it only be self, your call will be rejected.

class A
  def implicit
    private_method
  end
  
  def explicit
    self.private_method
  end
  
  private
  
  def private_method
    "Private called"
  end
end

A.new.implicit
# => "Private called"

A.new.explicit
# => NoMethod...

If your application exports CSV, be advised that Excel and other spreadsheet applications treat certain cells (those starting with =, +, - or @) as formulas.

This is an issue if you output user input. Not only is it probably not what you want, it also poses a security risk. See the link for attack vectors.

Note that current Excel versions will warn the user when opening the file. At least for the code execution vulnerability, these three warnings seems adequate to me.

Code execution warnings:

![Image](/makandra/47624/attach...

Background

After switching a project from Sprockets to Webpack, I started observing a bug that was hard to debug: Our custom icon font could sometimes not be displayed until a full page reload.

Digging deeper the only difference before and after the page load was the encoding interpretation of the iconfont stylesheet:

Correct representation (UTF-8):

.icon:before {
    content: ""
}

Broken representation (other charset):
`...