Here is what you can do on purpose to add several types of navigation in your React Native app:

import { createStackNavigator, createDrawerNavigator } from 'react-navigation';
import * as Screens from './screens/index';
import Drawer from './components/DrawerMenu';
import getDrawerWidth from './utils/scale';

const AppStackNavigator = createStackNavigator({
  home: {
    screen: Screens.MainScreen,
  },
  about: {
    screen: Screens.AboutScreen,
  },
});

const AppNavigator = createDrawerNavigator(
  {
    home: {
       screen: AppStackNavigator,
    },
  },
  {
    contentComponent: Drawer,
    drawerWidth: getDrawerWidth,
    headerMode: 'none',
  }
);

export default AppNavigator;

As it turned out, it’s pretty simple:

const user = { id: 1, name: 'Suhomozgy Andrey' }
const position = 'Frontend Developer'
const userWithPosition = {
  ...user,
  id: 2,
  ...(position && { position })
}

userWithPosition //=> { id: 2, name: 'Suhomozgy Andrey', position: 'Frontend Developer' }

# spec/rails_helper.rb
include ActionDispatch::TestProcess

In a factory, when setting the attribute value, use the method #fixture_file_upload, specifying the path and file type.

# spec/factories/import_file.rb
FactoryBot.define do
  factory :import_file, class: ImportFile do
    data { fixture_file_upload 'spec/fixtures/test_file.pdf', 'application/pdf' }
  end
end

Write a function that take array of functions and iterates each of them a certain number of times. Will use the difference in performance.now() values before and after to get the total time in milliseconds each iteration running.

Play with iterations argument to get more or less reliable results.

const mostPerformantFunction = (fns, iterations = 10000) => {
  const times = fns.map(fn => {
    const before = performance.now();
    for (let i = 0; i < iterations; i++) fn();
    return performance.now() - before;
  });
  console.log(times);
  return times.indexOf(Math.min(...times));
};

mostPerformantFunction([
  () => {
    [1, 2, 3, 4, 5, 6, 7, 8, 9, '10'].every(el => typeof el === 'number');
  },
  () => {
    [1, '2', 3, 4, 5, 6, 7, 8, 9, 10].every(el => typeof el === 'number');
  }
]); // 1

export function someFunction(values) {
  return (dispatch) => {
    ...
    const method = 'GET';
    const url = 'http://go.api/download_file';
    ...
    axios
      .request({
        url,
        method,
        responseType: 'blob', //important
      })
      .then(({ data }) => {
        const downloadUrl = window.URL.createObjectURL(new Blob([data]));
        const link = document.createElement('a');
        link.href = downloadUrl;
        link.setAttribute('download', 'file.zip'); //any other extension
        document.body.appendChild(link);
        link.click();
        link.remove();
      });
  };
}

env['api.tilt.template'] = 'foo/bar.json'

Then let’s define a render method in Base resourсe:

class Base < Grape::API
  def self.inherited(subclass)
    super

    subclass.instance_eval do
      helpers do
        def render(template_name)
          env['api.tilt.template'] = template_name
        end
      end
    end
  end
end

Now we can use it in the following way:

class ContactsResource < Base
  desc 'Create contact', http_codes: [[201, 'Created']]

  post '/contacts' do
    contact = Contact.new(params[:contact])

    if contact.save
      render 'v1/contacts/show.json'
    else
      error!({ errors: contact.errors.full_messages }, 422)
    end
  end
end

Rails.root + 'foo/bar'
[Rails.root, 'foo/bar'].join('/')
"#{Rails.root}/foo/bar"

But also there is a Pathname#/ method, so you can append string to route using a slash:

Rails.root/'foo/bar' # => #<Pathname:/Users/alex/myproject/foo/bar>

Looks more readable!

First line
Second line

To use “escape sequences” in a string literal you need to use an “extended” constant. You can specify the escape character by prefixing the letter E:

UPDATE posts SET body = E'First Line\nSecond line.' WHERE id = 2701;

  // App.js
  <Card size="sm">
    {/* ... */}
    <div>
      {/* ... */}
      <Button size="sm" onClick={action}>Action</Button>
    </div>
  </Card>

The size for both components is set by the “size” parameter. In the example above, the parameter passed is indicated for both components. In order not to specify the size for the Button each time, you can use the Context to use the one specified for the Card. If you use recompose, it can be super easy:

  // Card.js
  import { getContext } from 'recompose';
  // ...
  export default withContext(
    { size: PropTypes.oneOf(['sm', 'md', 'lg']) },
    ({ size }) => ({ size }),
  )(Card);
  
  // App.js
  import Button from './Button';
  // ...
  const EnhancedButton = getContext({ size: PropTypes.oneOf(['sm', 'md', 'lg']) })(Button);

Live example

a = true && false
a
=> false

a = true and false
a
=> true

The same situation could be reproduced for || and or. Why? The answer lies in Ruby Operator Precedence.

The first example can be represented as:

a = (true && false)

Second:

(a = true) and false

Thanks to Igor Alexandrov

Here is a way to do the exact that: You should pass your function as a parameter and after that just call it inside of the onChange method

Example:

const FormGroupAdapter = ({ input, inputOnChange }) => {
    const inputProps = {
        ...input,
        onChange: e => {
            input.onChange(e);
            inputOnChange && inputOnChange(e);
        }
    };

    return <input {...inputProps} />;
};

const handleChange = event => {
    console.log("!!!", event.target.value);
};

const App = () => (
    <Form
        ...
        render={({ handleSubmit, reset, submitting, pristine, values }) => (
            <form onSubmit={handleSubmit}>
                <div>
                    <label>some label</label>
                    <Field
                        name="someField"
                        component={FormGroupAdapter}
                        inputOnChange={handleChange}
                    />
                </div>
                ...
            </form>
        )}
    />
);

Live example

Here are a few reasons you may want to do that (borrowed from The Go Blog):

• easier to write: never worry about minor formatting concerns,
• easier to read: when all code looks the same you need not mentally convert others’ formatting style into something you can understand.
• easier to maintain: diffs show only the real changes.
• uncontroversial: never have a debate about spacing or brace position ever again

In fact, you actually want to format your Elixir code as you make it, meaning there is no need to format all of your project’s code every time.

The following bash command does it well on a single file: cd $projectPath && mix format $filePath

Where: $projectPath - full path to your project’s root directory; $filePath - full path to a file you’re saving

My IDE of choice happened to be Atom and I’ll talk briefly on setting it up. The Process Palette package so far is the best for this task. My Shell Command field (with variables) in Process Palette looks the following cd {projectPath} && mix format {fileAbsPath}

const toCurrency = (n, curr, LanguageFormat = undefined) =>
  Intl.NumberFormat(LanguageFormat, { style: 'currency', currency: curr }).format(n);

toCurrency(123456.789, 'EUR'); // €123,456.79  | currency: Euro | currencyLangFormat: Local
toCurrency(123456.789, 'RUB'); // RUB 123,456.79  | currency: Ruble | currencyLangFormat: Local
toCurrency(123456.789, 'RUB', 'Ru-ru') // 123 456,79 ₽  | currency: Ruble | currencyLangFormat: Russian
toCurrency(123456.789, 'USD', 'en-us'); // $123,456.79  | currency: US Dollar | currencyLangFormat: English (United States)
toCurrency(123456.789, 'USD', 'fa'); // ۱۲۳٬۴۵۶٫۷۹ ؜$ | currency: US Dollar | currencyLangFormat: Farsi
toCurrency(322342436423.2435, 'JPY'); // ¥322,342,436,423 | currency: Japanese Yen | currencyLangFormat: Local
toCurrency(322342436423.2435, 'JPY', 'fi'); // 322 342 436 423 ¥ | currency: Japanese Yen | currencyLangFormat: Finnish

Method try() comes from Active Support component of Ruby on Rails. Safe Navigation Operator is Ruby native feature.

Let’s check performance!

require 'benchmark'

class Foo
  attr_accessor :name
end

foo = Foo.new
bar = nil

Benchmark.bm(35) do |x|
  x.report('Successful access: try(...): ')         { 1_000_000.times { foo.try(:name) } }
  x.report('Successful access: &.: ')               { 1_000_000.times { foo&.name } }
  x.report('Successful access: control sample: ')   { 1_000_000.times { foo.name } }
  x.report('Failed access: try(...): ')             { 1_000_000.times { bar.try(:nonexistent) } }
  x.report('Failed access: safe navigation: ')      { 1_000_000.times { bar&.nonexistent } }
end;nil

                                          user     system      total        real
Successful access: try(...):          0.498216   0.005748   0.503964 (  0.530010)
Successful access: &.:                0.062146   0.000943   0.063089 (  0.069714)
Successful access: control sample:    0.062411   0.001098   0.063509 (  0.069603)
Failed access: try(...):              0.172535   0.004374   0.176909 (  0.194386)
Failed access: safe navigation:       0.054141   0.001029   0.055170 (  0.065502)

Safe navigation is about 7 times faster than method try() for successful navigation and 3 times faster for unsuccessful.

• Rails Method try(...)
• Safe Navigation Operator (&.)
• Logical operator && (AND)

Here is how these options look like:

user.try(:company).try(:name)

user&.company&.name

user && user.company && user.company.name

But there are some differences.

1. If model User hasn’t relation compppany (it may be just a typo or renamed model relation/attribute):

user.try(:compppany).try(:name)
=> nil

You will receive nil and never been know about this typo.

user&.compppany&.name
=> NoMethodError: undefined method `compppany' for #<User:0x000000123456789>

and

user && user.compppany && user.compppany.name
=> NoMethodError: undefined method `compppany' for #<User:0x000000123456789>

Looks better!

2. If model User has relation company, but company is false. User.new(company: false):

user.try(:company).try(:name)
=> nil

user&.company&.name
=> NoMethodError: undefined method `name' for false:FalseClass

Safe Navigation recognized false. Awesome!

user && user.company && user.company.name
=> false

Hmmm, it does not look like we want.

3. Performance Read the second part Safe Navigation vs Try in Rails (Part 2: Performance)

However, you can force file downloading instead of opening when an user clicks on the link though.

1st way (frontend):

HTML attribute download allows you to do this.

<a href="/public/report.pdf" download="stat_report">

If the value of the attribute is omitted, the original filename would be used. However, be careful. This attribute isn’t supported in some old browsers without HTML5 support. Renaming does not work if the given file stored on another host.

2nd way (backend):

You can set HTTP header Content-disposition.

for Nginx:

location ~* /public/(.+\.pdf)$ {
    add_header Content-disposition "attachment; filename=$1";
}

for Apache:

<IfModule mod_headers.c>
    <FilesMatch "\.(?i:pdf)$">
        ForceType application/octet-stream
        Header set Content-Disposition "attachment"
    </FilesMatch>
</IfModule>

class Trade < ActiveRecord::Base
  has_many :gl_entries, as: :source, dependent: :destroy
end

class GlEntry < ActiveRecord::Base
  belongs_to :source, polymorphic: true
end

You will not be able to add the usual foreign keys for cascading delete records. But this can be implemented using a database.

To do this, you need to write a trigger in the database that will run the delete function for each record.

CREATE FUNCTION deleteGlEntriesOfTrade()
  RETURNS TRIGGER
  SET SCHEMA 'public'
  LANGUAGE plpgsql 
  AS $$
  BEGIN
    DELETE FROM gl_entries WHERE source_id = OLD.id AND source_type = 'Trade';
    RETURN OLD;   
  END;
  $$;
      
CREATE TRIGGER deleteTradesGlEntriesTrigger 
  BEFORE DELETE ON trades
  FOR EACH ROW EXECUTE PROCEDURE deleteGlEntriesOfTrade();

Create a migration and use :)

To get statistics (number of tasks) by each queue:

Sidekiq::Stats.new.queues
=> {"local_cache"=>0, "default"=>0, "ts_delta"=>0, "mailchimp"=>0, "recorder"=>0}

Global statistics are available this way:

Sidekiq::Stats.new.fetch_stats!
=> {:processed=>61390,
 :failed=>3220,
 :scheduled_size=>0,
 :retry_size=>0,
 :dead_size=>4,
 :processes_size=>1,
 :default_queue_latency=>0,
 :workers_size=>0,
 :enqueued=>0}

The same stats are available separately:

stats = Sidekiq::Stats.new
stats.processed # number of processed tasks
stats.failed # number of failed tasks
stats.enqueued # number of enqueued tasks

and etc.

Also Sidekiq::Stats allows to look historical data. You can specify period. Something like:

s = Sidekiq::Stats::History.new(2, Date.parse('2019-02-05'))

• first argument: number of days,
• second argument: date until which return stats (default value is today and can be omitted)

s.processed
=> {"2019-02-05"=>0, "2019-02-04"=>0}
s.failed
=> {"2019-02-05"=>0, "2019-02-04"=>0}

To clean refs to nonexistent branches in the remote:

$ git fetch --prune

--prune before fetching, remove any remote-tracking references that no longer exist on the remote.

To estimate how many branches merged into dev:

$ git branch --merged dev | wc -l

--merged option can filter list to branches that you have merged into the given branch. Squash and rebase merges usually aren’t detected by --merged.

List of branches merged into dev:

$ git branch --merged dev

List of remote branches merged into dev:

$ git branch --merged dev --remote

If you are courageous then:

$ git branch --merged dev | egrep -v "(^\*|master|dev)" | xargs git branch -d

It removes all local branches that merged into dev (except dev and master). This is a potentially damaging operation. It can delete branches actually needed. So if you use the different approach to work with Git, you could remove some of branches manually instead. I hope you do not store all old branches, do you?

def application_klass
  @application_klass ||= "application/#{params[:type]}".classify.constantize
end

There are Application::Rental and Application::Bridge models in our rails app, so the method above was used in two places:

1. application_klass.to_s – to get the model name as a string
2. application_klass.model_name.human – to get a class name without module prefix

I’ve refactored method in the following way:

def application_klass
  @application_klass ||= "application/#{params[:type]}".classify
end 

And it’s occurrences now looks like this:

1. application_klass – just call this method to get a model name
2. application_klass.demodulize – using demodulize to split a string with ::

I’ve got rid of unnecessary constantize method, which is quite inefficient: just imagine that your application tries to find a constant in your project with the name specified in the string. See the benchmarks below to evaluate performance gains:

counter = 100_000
type = 'Rental'

Benchmark.bm(30) do |x|
  x.report('demodulize: ')                   { counter.times { "application/#{type}".classify.demodulize } }
  x.report('constantize.model_name.human: ') { counter.times { "application/#{type}".classify.constantize.model_name.human } }
end

                                     user     system      total        real
demodulize:                      3.560000   0.760000   4.320000 (  4.381891)
constantize.model_name.human:    8.500000   0.070000   8.570000 (  8.601007)

def realizing_trade_type(realizable_trade_type)
  case realizable_trade_type
  when 'buy'
    'sell'
  when 'short'
    'cover'
  when 'buy_contract'
    'sell_contract'
  when 'short_contract'
    'cover_contract'
  end
end

But, if the conditions and the results are simple values, why don’t we use hash for this? We can :)

REALIZING_TRADE_TYPES = {
  'buy'            => 'sell',
  'short'          => 'cover',
  'buy_contract'   => 'sell_contract',
  'short_contract' => 'cover_contract'
}.freeze

Here is the benchmark of both options, executed 10_000_000 times. It shows that a hash is faster in times for such the kind of usage.

>> require 'benchmark'
true
>> Benchmark.bm(15) do |x|
  x.report('hash') { 10_000_000.times { REALIZING_TRADE_TYPES['buy'] } }
  x.report('case-statement') { 10_000_000.times { realizing_trade_type 'buy' } }
  x.report('empty') { 10_000_000.times {} }
end
                      user     system      total        real
hash              0.990423   0.003412   0.993835 (  1.057612)
case-statement    1.752263   0.004531   1.756794 (  1.762030)
empty             0.380810   0.000728   0.381538 (  0.382153)

So, it’s better to use a hash when you are just retrieving some values (like in the example above). If there is additional logic to execute, a case-statement is still a way to go.

The answer is pretty simple: you work with them like with nested attributes.

Let’s say, we have class Provider with attribute address.

class Provider < ApplicationRecord
  attribute :address, Provider::Address::Type.new, default: Provider::Address.new

Address has following attributes:

class Provider::Address
  extend Dry::Initializer

  option :country, optional: true
  option :zip, optional: true
  option :city, optional: true
  option :address, optional: true

Form will look like this:

= form_for resource_provider, provider_url do |f|
  = f.fields_for :address do |ff|
      = ff.label 'Country'
      = ff.text_field :country, value: @provider.billing_address.country
      
      = ff.label 'Zip'
      = ff.text_field :zip, value: @provider.billing_address.zip
      
      = ff.label 'City'
      = ff.text_field :city, value: @provider.billing_address.city
      
      = ff.label 'Address'
      = ff.text_field :address, value: @provider.billing_address.address

In controller you have to permit parameters:

def provider_params
    params.require(:provider).permit(address: [:city, :zip, :country, :address])
end

And that’s all. Now, in action method you can assign attributes like this:

resource_provider.attributes = provider_params
resource_provider.save

It turns out that localStorage raises events 😍

Namely, events are triggered when an item is added, deleted, or changed in another context. In essence, this means that when you change localStorage in one tab, other tabs can find out about this by listening to the storage event of the global window object. For example:

  window.addEventListener('storage', function (event) {
    console.log(event.key, event.newValue);
  });

Of course, there are some restrictions on use (you can read about them here https://www.w3.org/TR/webstorage/), but for simple cases it is match perfect.

Lets create function to do that:

const renameKey = (object, key, newKey) => {
  const clonedObj = clone(object);
  const targetKey = clonedObj[key];

  delete clonedObj[key];
  clonedObj[newKey] = targetKey;
  return clonedObj;
};

Here is clone function:

const clone = (obj) => Object.assign({}, obj);

Example:

let contact = { 
    id: 1, 
    name: "contact name"
};

contact = renameKey(contact, 'id', 'value');
contact = renameKey(contact, 'name', 'label');

console.log(contact); // { value: 1, label: "contact name" };