Learn Http, Immutable and Radium

In this course, we will learn the fundamentals of the Hypertext Transport Protocol (HTTP) by exploring several popular HTTP APIs such as the GitHub API. Starting with the basic structure of an HTTP request and response, we will then delve into the specifics of each element of the request/response messages. Using concrete examples from these APIs, we will cover request methods, response status codes, messages headers, and message bodies. Along the way, you'll learn about specific message headers, such as `Cache-Control`, and `Cookie`  and how they control the behavior of clients/browsers and HTTP API services.

This course uses HTTPie, if you would like to follow along with the instructor you can download the client [here](https://httpie.org/).

The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. It is a generic, stateless, protocol which can be used for many tasks beyond its use for hypertext, such as name servers and distributed object management systems, through extension of its request methods, error codes and headers.

http

Understand the Basics of HTTP

im·mu·ta·ble i(m)ˈmyo͞odəb(ə)l/ adjective - **unchanging over time or unable to be changed**.

Mutating data is the source of never ending headaches in software systems, and JavaScript code is no exception. Immutable data structures, pure functions, uni-directional data flow... you've probably been hearing these terms.

Immutable.js provides us the data structures and utilities that we need to start introducing this powerful concept of immutability into our applications.

Immutable.js provides many Persistent Immutable data structures including: List, Stack, Map, OrderedMap, Set, OrderedSet and Record.

immutable

Learn how to use Immutable.js

As developers, we're often working closely with APIs to make requests in the browser or on the backend with a server, but we might not always know exactly how those requests work or how they should look.

Postman is a tool that lets us create, manage, and test API endpoints all within a UI so we can wrangle our APIs and understand how they work.

Create, Manage, and Test API Requests with Postman

Immutable.js offers methods to break  immutable structures into subsets much like Array--for instance it has the all powerful slice()--and unlike Array it offers functional methods like take() and skip(). You get the best of both the imperative and functional worlds.

Working with Subsets of an Immutable.js Map()

Equality checking deeply nested objects is painful. Fortunately Immutable.js makes this task easy with its .is() and .isSubset() methods. Let's see how we can take two different Immutable Maps() and check for equality.

Equality Checking with .is() and More

Immutable.js offers the fromJS() method to build immutable structures from objects and array. Objects are converted into maps. Arrays are converted into lists. The fromJS() method can also take a reviver function for custom conversions.

Using fromJS() to Convert Plain JavaScript Objects into Immutable Data

Understanding Immutable.js's Map() and List() structures will likely take you as far as you want to go with immutable programming. They have only small semantic differences between each other and the remaining structures in the Immutable.js family. Sequence, however, has one major difference: it's lazy--which opens a new realm of functional possibilities. Let's write a simple sequence to start.

Exploring Sequences and Range() in Immutable.js

Immutable.js iterables offer the reduce() method, a powerful and often misunderstood functional operator on which map(), filter(), groupBy(), etc. are built. The concept is simple: reduce transforms your iterable into something else, that's all. The name is misleading as you may or may not actually "reduce" anything. Let's replicate the groupBy() and filter() methods with reduce to illustrate how it works.

Transforming Immutable Data with Reduce

While Immutable.js offers .is() to confirm value equality between iterables it comes at the cost of referencing each key and value in both objects. For lightning fast equality checks, Immutable.js can produce a hash code based on an iterable's content. If two iterables have the same content, their hash codes will be the same. It's worth noting that this technique is unsuitable for mission critical application development since there is a chance, however slight, that checksums like these might collide. This is outlined here: https://en.wikipedia.org/wiki/Collision_(computer_science)

Lightning Fast Immutable.js Equality Checks with Hash Codes

The Immutable.js Record() allows you to model your immutable data much like you would model data with native Javascript classes or objects. It differs from native classes because it cannot be mutated after it's creation and it *always* has a default value. It's an excellent construct in which to piece together your stores, be them Flux or some other storage implementation. Let's quickly create an Immutable Record().

Immutable.Record() as data models

The HTTP GET & HEAD methods are used to retrieve information about a resource. The GET method will retrieve the metadata about the resource, encoded in the HTTP headers, as well as a representation of the resource itself in the message body (e.g. a JSON document with fields that describe a user). The HEAD method behaves like GET, but only retrieves the status and headers; this can be useful when you need some metadata about a resource (e.g. the Last-Modification time), but don't want to waste time or bandwidth fetch the resource itself in the message body. Finally, we discuss the idempotent and safe natures of these HTTP methods.

Use HTTP GET & HEAD Methods

The 2xx family of status codes are used in HTTP responses to indicate success. Beyond the generic `200 OK` status code, there are a set of more specific success status codes that provide additional context or details about the specific nature of the successful request/response. We will explore the available success status codes, and what additional information they convey.

Understand 2xx HTTP Status Code Responses

The body of an HTTP request or response can serve many functions, from including the input data to a POST request, to returning varied representations of a resource in response to a GET request. This lesson details how message bodies are handled in requests and responses, and the associated HTTP headers that provide metadata about the included message body.

Examine HTTP Message Bodies

The HTTP DELETE method is used to request that the server perform a delete operation on the specified resource with resource specific semantics. Behind the scenes, the delete operation may result in a removal of a file from the filesystem, or an update to the database to reflect the change. Because multiple requests to delete the same resource has the same effect as a single one, the DELETE method is considered ‘idempotent’, but not considered safe.

Use HTTP DELETE Method

The HTTP OPTIONS method is used to request information about the communication options available for the target resource. The response may include an Allow header indicating allowed HTTP methods on the resource, or various Cross Origin Resource Sharing headers. The HTTP OPTIONS method is both safe and idempotent, as it is intended only for use in querying information about ways to interact with a resource.

Use HTTP OPTIONS Method

The HTTP PATCH method is used to make modifications to existing resources. In particular, it is designed for "partial updates", as opposed to replacing an entire resource using the HTTP PUT method. Although certain HTTP PATCH requests may behave idempotently, this is not true of all possible PATCH requests, so this request method is not idempotent, nor considered safe. The request body of a PATCH request may be simple `application/json`, or a more specialized type, such as `application/json-patch+json`.

Use HTTP PATCH Method

The HTTP POST method is used to request the resource process the included request message body representation according to resource specific semantics. HTTP POST is loosely defined by definition, and can be used in many different scenarios, such as creating a new resource based on the request representation, appending data to an existing representation, or generic processing of an HTML form submission. Due to the nature of POST performing arbitrary resource specific processing, it is considered neither ‘safe’, nor ‘idempotent’.

Use HTTP POST Method

The 4xx family of status codes are used in HTTP responses to inform the client/browser of an error relating to the user’s request. The status codes in this family are intended to indicate a problem that should be possible to fix or remedy by the user or developer. For example, a 401 Unauthorized status code lets the user/developer know they need to provide authorization information with their request; should they re-submit the request with the additional authorization header, the request may succeed. We will explore the available client error status codes, and what additional information they convey.

Understand HTTP 4xx Client Error Response Codes

The 5xx family of status codes are used in HTTP responses to inform the client that the server experienced an error. The status codes in this family are intended to indicate server or network errors that do not pertaining to a problem with client or the client’s request. For example, a response with a 503 Service Unavailable status code is unlikely to be resolved by resubmitting the request with different content type or additional headers. We will explore the available server error status codes, and what additional information they convey.

Understand 5xx Server Error Response Codes

Previously to tackle manual restarts due to server crashes , process management tools were used. 

Forever is one such module that is runs on the node ecosystem. So, we need not move away from the rich ecosystem of Node.js.

Use ``` npm install --global forever ``` to install forever module globally.
 

Running your server forever using forever in Node.js

Understand the three basic parts of making HTTP requests in Elm: 1) Building the request, 2) Writing a JSON decoder, 3) Sending the request using the Elm runtime, and reacting to the results with messages.

HTTP requests are just pieces of data in Elm. When we want to send them, we hand them off to Elm's runtime, and it notifies us when the request is done. An important part of working with HTTP requests that fetch JSON is JSON decoding, the process by which we can turn untyped JSON data into Elm types that are safe to work with.

Specs:

- Editor: Atom
- Theme: [Nebula (with Nebula syntax theme)](https://atom.io/themes/nebula-ui)
- Font: [Iosevka with ligatures enabled](https://github.com/be5invis/Iosevka)
- Plugin used for imports: [Elmjutsu](https://atom.io/packages/elmjutsu)
- Plugin used for formatting: [Elm-format](https://atom.io/packages/elm-format)
- Plugin used for linting: [linter-elm-make](https://atom.io/packages/linter-elm-make)


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