Tutorial by Examples: id

Errors and error middleware

If we would like to limit the access to our app, we could write a middleware for that too! This example only grants you access on thrusdays, but a real world example could, for example, be user authentication. A good place to put this would be after the logging middleware but before any content is s...

express • Connect

Send messages from JavaScript and Handle them on the native side

Messages can be sent from JavaScript using the following code window.webkit.messageHandlers.{NAME}.postMessage() Here how to create a script message handler to handle the messages: class NotificationScriptMessageHandler: NSObject, WKScriptMessageHandler { func userContentController(userCon...

iOS • WKWebView

Width vs Viewport

When we are using "width" with media queries it is important to set the meta tag correctly. Basic meta tag looks like this and it needs to be put inside the <head> tag. <meta name="viewport" content="width=device-width,initial-scale=1"> Why this is impo...

CSS • Media Queries

Overriding hash function

Ruby hashes use the methods hash and eql? to perform the hash operation and assign objects stored in the hash to internal hash bins. The default implementation of hash in Ruby is the murmur hash function over all member fields of the hashed object. To override this behavior it is possible to overrid...

Ruby Language • Hashes

Page width and height

To get current page width and height (for any browser), e.g. when programming responsiveness: function pageWidth() { return window.innerWidth != null? window.innerWidth : document.documentElement && document.documentElement.clientWidth ? document.documentElement.clientWidth : document.bo...

JavaScript • Screen

Using formidable module

Install module and read docs npm i formidable@latest Example of server on 8080 port var formidable = require('formidable'), http = require('http'), util = require('util'); http.createServer(function(req, res) { if (req.url == '/upload' && req.method.toLowerCase() == 'pos...

Node.js • File upload

Managing local notifications using UUID

Often times you will need to be able to manage your notifications, by being able to keep track of them and cancel them. Track a notification You can assign a UUID (universally unique identifier) to a notification, so you can track it: Swift let notification = UILocalNotification() let uuid = NS...

iOS • UILocalNotification

IDEs

A list of available IDEs to create classes, triggers, Visualforce/Lightning pages/components. Force.com IDE – plugin for Eclipse JedIDE – plugin for IntelliJ IDEA & standalone Force.com IDE MavensMate – plugin for Sublime Text and Atom and VS Code FuseIT SFDC Explorer - This is a standalon...

Salesforce • Tools for Development

Lazily flattening a multidimensional Array with flatten()

We can use flatten() in order to lazily reduce the nesting of a multi-dimensional sequence. For example, lazy flattening a 2D array into a 1D array: // A 2D array of type [[Int]] let array2D = [[1, 3], [4], [6, 8, 10], [11]] // A FlattenBidirectionalCollection<[[Int]]> let lazilyFlatten...

Swift Language • Arrays

Going from wide to long format using melt

Melting: The basics Melting is used to transform data from wide to long format. Starting with a wide data set: DT = data.table(ID = letters[1:3], Age = 20:22, OB_A = 1:3, OB_B = 4:6, OB_C = 7:9) We can melt our data using the melt function in data.table. This returns another data.table in long...

data.table • Reshaping, stacking and splitting

pubnub access manager at server side

PubNub Access Manager (PAM) extends PubNub's existing security framework by allowing developers to create and enforce secure access to channels throughout the PubNub Real Time Network. Access Manager allows you to manage granular permissions for your realtime apps and data streams, create multiple ...

PubNub • Access Manager

Validates format of an attribute

Validate that an attribute's value matches a regular expression using format and the with option. class User < ApplicationRecord validates :name, format: { with: /\A\w{6,10}\z/ } end You can also define a constant and set its value to a regular expression and pass it to the with: option. ...

Ruby on Rails • ActiveRecord Validations

Validates inclusion of an attribute

You can check if a value is included in an array using the inclusion: helper. The :in option and its alias, :within show the set of acceptable values. class Country < ApplicationRecord validates :continent, inclusion: { in: %w(Africa Antartica Asia Australia ...

Ruby on Rails • ActiveRecord Validations

Hide blinking caret

To hide the blinking caret, you need to override caretRectForPosition of a UITextField and return CGRectZero. Swift 2.3 < public override func caretRectForPosition(position: UITextPosition) -> CGRect { return CGRectZero } Swift 3 override func caretRect(for position: UITextPositio...

iOS • UITextField

Middleware

Middleware (also called pre and post hooks) are functions which are passed control during execution of asynchronous functions. Middleware is specified on the schema level and is useful for writing plugins. Mongoose 4.0 has 2 types of middleware: document middleware and query middleware. Document mid...

mongoose • mongoose pre and post middleware (hooks)

Avoiding NullReferenceException

7.0 OrElse Sub Main() Dim elements As List(Of Integer) = Nothing Dim average As Double = AverageElementsOrElse(elements) Console.WriteLine(average) ' Writes 0 to Console Try 'Throws ArgumentNullException average = AverageElementsOr(elements) Catch ex ...

Visual Basic .NET Language • Short-Circuiting Operators (AndAlso - OrElse)

Avoid qualifying a nested type name

class ClassWithAReallyLongName { public: class Iterator { /* ... */ }; Iterator end(); }; Defining the member end with a trailing return type: auto ClassWithAReallyLongName::end() -> Iterator { return Iterator(); } Defining the member end without a trailing return type: Clas...

C++ • Trailing return type

Pandas melt to go from wide to long

>>> df ID Year Jan_salary Feb_salary Mar_salary 0 1 2016 4500 4200 4700 1 2 2016 3800 3600 4400 2 3 2016 5500 5200 5300 >>> melted_df = pd.melt(df,id_vars=['ID','Year'], v...

pandas • Reshaping and pivoting

How to pick image and video for api >19

Here is a tested code for image and video.It will work for all APIs less than 19 and greater than 19 as well. Image: if (Build.VERSION.SDK_INT <= 19) { Intent i = new Intent(); i.setType("image/*"); i.setAction...

Android • Android Sound and Media

Abstracts for data validation

The following abstract defines an EmailAddress type based on the String type which will use a regular expression to validate the passed argument as an e-mail address. If the address isn't valid, an exception will be thrown. abstract EmailAddress(String) { static var ereg = ~/^[\w-\.]{2,}@[\w-\.]...

haxe • Abstracts