Tutorial by Examples: an

Handling Exception In Node.Js

Node.js has 3 basic ways to handle exceptions/errors: try-catch block error as the first argument to a callback emit an error event using eventEmitter try-catch is used to catch the exceptions thrown from the synchronous code execution. If the caller (or the caller's caller, ...) used try/ca...

Node.js • Exception handling

Log for a range of lines within a file

$ git log -L 1,20:index.html commit 6a57fde739de66293231f6204cbd8b2feca3a869 Author: John Doe <[email protected]> Date: Tue Mar 22 16:33:42 2016 -0500 commit message diff --git a/index.html b/index.html --- a/index.html +++ b/index.html @@ -1,17 +1,20 @@ <!DOCTYPE HTML> ...

Git • Browsing the history

Changing the author of commits

You can use an environment filter to change the author of commits. Just modify and export $GIT_AUTHOR_NAME in the script to change who authored the commit. Create a file filter.sh with contents like so: if [ "$GIT_AUTHOR_NAME" = "Author to Change From" ] then export GIT_A...

Git • Rewriting history with filter-branch

Taking a screenshot and video (for kitkat only) from a device display

Screen shot: Option 1 (pure adb) The shell adb command allows us to execute commands using a device's built-in shell. The screencap shell command captures the content currently visible on a device and saves it into a given image file, e.g. /sdcard/screen.png: adb shell screencap /sdcard/screen.png...

Android • ADB (Android Debug Bridge)

Russian Doll Caching

You may want to nest cached fragments inside other cached fragments. This is called Russian doll caching. The advantage of Russian doll caching is that if a single product is updated, all the other inner fragments can be reused when regenerating the outer fragment. As explained in the previous sec...

Ruby on Rails • Caching

The has_many :through association

A has_many :through association is often used to set up a many-to-many connection with another model. This association indicates that the declaring model can be matched with zero or more instances of another model by proceeding through a third model. For example, consider a medical practice where p...

Ruby on Rails • ActiveRecord Associations

The has_and_belongs_to_many association

A has_and_belongs_to_many association creates a direct many-to-many connection with another model, with no intervening model. For example, if your application includes assemblies and parts, with each assembly having many parts and each part appearing in many assemblies, you could declare the models...

Ruby on Rails • ActiveRecord Associations

Get first and last record

Rails have very easy way to get first and last record from database. To get the first record from users table we need to type following command: User.first It will generate following sql query: SELECT `users`.* FROM `users` ORDER BY `users`.`id` ASC LIMIT 1 And will return following recor...

Ruby on Rails • ActiveRecord Query Interface

RankNTypes

Imagine the following situation: foo :: Show a => (a -> String) -> String -> Int -> IO () foo show' string int = do putStrLn (show' string) putStrLn (show' int) Here, we want to pass in a function that converts a value into a String, apply that function to both a string p...

Haskell Language • Common GHC Language Extensions

Generating a new mailer

To generate a new mailer, enter the following command rails generate mailer PostMailer This will generate a blank template file in app/mailers/post_mailer.rb named PostMailer class PostMailer < ApplicationMailer end Two layout files will also be generated for the email view, one for the...

Ruby on Rails • ActionMailer

Using Grand Central Dispatch (GCD)

GCD will guarantee that your singleton only gets instantiated once, even if called from multiple threads. Insert this into any class for a singleton instance called shared. + (instancetype)shared { // Variable that will point to the singleton instance. The `static` // modifier makes it ...

Objective-C Language • Singletons

Depend on Another Gradle Project

In the case of a multi-project gradle build, you may sometimes need to depend on another project in your build. To accomplish this, you'd enter the following in your project's dependencies: dependencies { compile project(':OtherProject') } Where ':OtherProject' is the gradle path for the p...

gradle • Dependencies

Manually Testing Your Models

Testing your Active Record models through your command line interface is simple. Navigate to the app directory in your terminal and type in rails console to start the Rails console. From here, you can run active record methods on your database. For example, if you had a database schema with a User...

Ruby on Rails • ActiveRecord

The Bitwise and Logical Operators (~, &, |, ^)

The Java language provides 4 operators that perform bitwise or logical operations on integer or boolean operands. The complement (~) operator is a unary operator that performs a bitwise or logical inversion of the bits of one operand; see JLS 15.15.5.. The AND (&) operator is a binary operat...

Java Language • Operators

Panel with heading

Easily add a heading container to your panel with .panel-heading. You may also include any <h1>-<h6> with a .panel-title class to add a pre-styled heading. However, the font sizes of <h1>-<h6> are overridden by .panel-heading. For proper link coloring, be sure to place links...

twitter-bootstrap • Panels

Panel with footer

Wrap buttons or secondary text in .panel-footer. Note that panel footers do not inherit colors and borders when using contextual variations as they are not meant to be in the foreground. <div class="panel panel-default"> <div class="panel-body"> Panel content...

twitter-bootstrap • Panels

Pre-decode a field and decode the rest depending on that decoded value

The following examples can be tested on https://ellie-app.com/m9vmQ8NcMc/0. import Html exposing (..) import Json.Decode payload = """ [ { "bark": true, "tag": "dog", "name": "Zap", "playful": true } , { "w...

Elm Language • Json.Decode

Declaring content scripts in the manifest

Content scripts can be declared in manifest.json to be always injected into pages that match a set of URL patterns. Minimal example "content_scripts" : [ { "js": ["content.js"], "css": ["content.css"] "matches": [&quot...

google-chrome-extension • Content scripts

Injecting content scripts from an extension page

If, instead of always having a content script injected based on the URL, you want to directly control when a content script is injected, you can use Programmatic Injection. Minimal example JavaScript chrome.tabs.executeScript({file: "content.js"}); CSS chrome.tabs.insert...

google-chrome-extension • Content scripts

Multiple content scripts in the manifest

Same conditions, multiple scripts If you need to inject multiple files with all other conditions being the same, for example to include a library, you can list all of them in the "js" array: "content_scripts" : [ { "js": ["library.js", "conten...

google-chrome-extension • Content scripts