# Ethos

Intuitive state management for React.

Why Ethos?

• Intuitive
  • Ethos is easy to learn and incrementally adoptable.
• Fast
  • Not only can Ethos dramatically speed up your development process, it also beats Flux on benchmarks such as script evaluation, compile time and lifecycle iteration.
• Powerful
  • Ethos gives your data leverage with responsive features such as computed properties (thoughts) and watcher functions.

Getting Started

This tutorial will walk you through using Ethos with React.

Installation

	npm install ethos --save

or

	yarn add ethos

Principles

Ethos is built on the principle of a Single Source of Truth. To keep users mindful of this ideology, we’ve chosen to rename the popular Store and state to Source and truth.

Truth

Truth is the most important property in the Ethos Source. It holds all the data.

Defining Truth

Defining truth in Ethos is simple:

	// ./source.js
	
	import Ethos, { Source } from 'ethos'

  let count = 0;
  function id(){
    count++
    return count;
  }
	const source = {
		truth:{
			todos:[
				{
				  	text:"take out the trash",
          		id:id(), //1
					complete:false,
				},
				{
          		text:"clean room",
          		id:id(), //2
					complete:false,
        		},
				{
          		text:"feed dog",
          		id:id(), //3
					complete:false,
        		}
			],
			time:Date.now()
		}
	}

	export default new Source(source);

Accessing Truth

source.getTruth()

Truth is accessed outside the source by using a Source prototype method called getTruth

• getTruth takes in two arguments:
  1. The first argument is a query for which truth properties you want. This can be an array or an object:
     • With an Array, as in the example below, each string item represents both the name of your source's truth prop and the property it will be returned as.
       • e.g. let localTruth = getTruth(['todos'], this) can be used as localtruth.todos .
  • With an Object, you can alias a source's truth properties with whatever you want by using a key of your custom name with a value of the actual property name. - e.g. If you wanted 'todos' to be aliased as 'myTodos', you could use let localTruth = getTruth({ myTodos: 'todos' }) then reference it as localTruth.myTodos .

2. The second argument is the component itself, this. It essentially tells Ethos to watch the component and update it when something changes.

Full Example:

	// ./my-component.js
	import React from 'react';
	import source from './source.js';

	export default class TodoList extends React.Component {
		constructor(props){
		   super(props);
		   this.truth = source.getTruth(['todos'], this);
		}
		
		render(){
			return (

          <ul id="todo-list">
            {this.truth.todos.map((todo, index)=> (
              <li
                key={todo.id}
              >
				{todo.text}
				</li>
            ))}
          </ul>

			)
		}
	}

Note that getTruth returns an object of getters, so Object.assign and the object rest spread operator will not work with the returned object.

Writers

This is great, but truth is constantly changing. In Ethos, truth is updated with writers.

The formatting for writers isn't much different than truth, but there's a bit more going on here:

	// ./source.js
	
	import Ethos, { Source } from 'ethos'

  let count = 0;
  function id(){
    count++;
    return count;
  }
	const source = {
		truth:{...}, // Same as above

		writers:{
			addTodo(text){
				let todo = { 
					text:text, 
					id:id(),
					complete:false,
				}
				this.truth.todos.push(todo);
			},
			completeTodo(index){
				let todo = this.truth.todos[index];
				todo.complete = true;
			}
		},
	}

	export default new Source(source);

What’s this?

To avoid some pains of other systems, Ethos binds your writers to a snapshot of your Source. This makes it possible for writer functions to accept as many arguments as necessary.

• this.truth is your Source’s truth property, there for you to access and change it as you please.
• this.writers are your Source’s writers.
• this.runners are your Source’s runners. (more on this in a bit)
• this.write is your Source’s write method. 〃 〃
• this.run is your Source’s run method. 〃 〃

Running Writers

The easiest way to invoke a writer is to access it in source.writers.

	// ./my-component.js
	import React from 'react';
	import source from './source.js';

	export default class TodoList extends React.Component {
		constructor(props){
		   super(props);
		    this.truth = source.getTruth(['todos'], this)
		}

		addTodo(text){
			source.writers.addTodo(text)
		}
		
		completeTodo(index){
			source.writers.completeTodo(index)
		}

		render(){
			return (

          <ul id="todo-list">
            {this.truth.todos.map((todo, index)=> (
              <li
             		key={todo.id}
					onClick={()=>this.completeTodo(index)}
              >
					{todo.text}
				</li>
            ))}
          </ul>

			)
		}
	}

There’s another way to invoke a writer: the write method. source.write takes in two arguments. The first is the writer’s name and the second is the argument you want to pass to the writer.

Hence, addTodo above could be rewritten as

...
		addTodo(text){
			source.write('addTodo', text)
		}
...

Both methods provide the same functionality. Using write, however, limits you to one argument. The latter method may look a bit more familiar if you’re coming from flux/redux.

Runners

Writers have one catch: they update your components synchronously. This means asynchronous changes ( made via API calls, WebSockets, or setTimeouts, etc. ) may not have updated truth by the time Ethos updates your components.

To solve this problem, we have runners. Ethos runners handle all asynchronous activity in the source. Put simply, runners run other functions.

You may have noticed we already have a time property in the truth of our example. Let’s make it update once per second.

	// ./source.js
	
	import Ethos, { Source } from 'ethos'
	
	const source = {
		truth:{
			todos:[...], // Same as above
			time:Date.now()
		},
		
		writers:{
			... // Same as above
			updateTime(){
				this.truth.time = Date.now();
			}
		},
			
		runners:{
			initTime(){
				let timeout = setInterval(()=>{
					/* this will run once per second */
					this.writers.updateTime();
				}, 1000)
			}
		}
		
	}

	export default new Source(source);

What’s this?

Similarly to writers, runners are bound to a snapshot representing functionality in your Source. Runners’ snapshot is slightly different, however.

• this.writers are your Source’s writers.
• this.runners are your Source’s runners.
• this.write is your Source’s write method.
• this.run is your Source’s run method. ( we’ll get to this in a second )

Truth & Done

While runners also have access to truth , any mutations made to truth will not sync without use of the done method.

• this.truth is your Source’s truth.
• this.done is a method which tells your source that you mutated truth, and the source needs to update accordingly.

This enables you to avoid writing tedious writers which simply change a value.

See an example of this.done() in Examples below.

this.done is an experimental feature and disabling it will be possible with the upcoming strict mode.

Promise Wrappers

Ethos also gives you the ability to wrap any runner in an ES6 Promise using this.async(), this.resolve() and this.reject(). Promises can get quite verbose. Promise wrappers aim to fix that.

• this.async() is the method which initializes the Promise wrapper. It must be invoked outside your asynchronous code.
• this.resolve() is the Promise’s resolve function.
• this.reject() is the Promise’s reject function. See an example of Promise wrappers in Examples below.

Running Runners

Now, our initTime function won’t run itself. (though technically, it could 🙃)

The easiest way to invoke a runner is to access it in source.runners.

	source.runners.initTime()

Just like with writers, there’s another way to invoke a runner: the run method. source.run takes in two arguments. The first is the function name and the second is the payload, a lone object.

Hence, the above code could also be written as

...
	source.run('initTime')
...

The same principles apply for run as those for write.

Examples

Mutating truth with this.done()

	...
		runners:{
			initTime(){
				let timeout = setInterval(()=>{
					/* this will run once per second */
					this.truth.time = Date.now();
					this.done()
				}, 1000)
			}
		}
	...

Using Promise Wrappers

This example handles a simple GET request to the Giphy API using the popular HTTP client, Axios.

		...
  	runners:{
		getRandomGifUrl(){
        /*
        1. Initialize the Promise wrapper *outside* the
           asynchronous code.
        */
        this.async();

        let baseUrl = 'http://api.giphy.com/v1/gifs/random';

		  axios.get(baseUrl + '?api_key=dc6zaTOxFJmzC&tag=ethos')
		  .then((res)=>{
            let imageUrl = res.data.data.image_url;
            // resolves promise
            this.resolve(imageUrl);
		  })
        .catch((error)=>{
          // rejects promise
          this.reject(error);
        })
		}
	}
	...

Now when getRandomGifUrl runs, it will return a Promise. The following will be possible:

	let defaultImageUrl = 'https://media.giphy.com/media/UbQs9noXwuSFa/giphy.gif?response_id=591ccaaaecadb1fa9e03044c'
	source.runners.getRandomGifUrl()
	.then((imageUrl)=>{
		/* 
		imagine you have a function which changes the 
		source of an image
		*/
		setImageSrc(imageUrl)
	})
	.catch((error)=>{
		setImageSrc(defaultImageUrl)
	})

In many cases, using async and await is the optimal path, but Promise wrappers are nice for when your asynchronous code doesn’t already utilize promises.

Watchers

A watcher is a function that is invoked whenever a property on truth changes. Watchers are defined like so:

	// ./source.js
	
	import Ethos, { Source } from 'ethos'
	
	const source = {
		truth:{
			todos:[...], // Same as above
			time:Date.now()
		},
		
		writers:{...}, // Same as above
			
		runners:{...}, // Same as above
		
		watchers:{
			todos(){
				/* 
				this will run every time 
				something changes in `truth.todos`
				*/
				console.log('Todos changed!')
			}
		}
	}

	export default new Source(source);

What’s this?

this for watchers is the same as this for writers

• this.truth is your Source’s truth property.
  • It’s not suggested that you directly mutate truth from watchers.
• this.writers are your Source’s writers.
• this.runners are your Source’s runners.
• this.write is your Source’s write method.
• this.run is your Source’s run method.

Thoughts

Thoughts observe one or more pieces of truth, combine it with some custom logic, and return a new piece of truth. When a piece of truth a thought is observing changes, the thought will update its value. Let’s say we have two numbers, a and b, in our truth.

...
      truth:{
        a:1,
        b:2,
      },
      writers:{
        addOneToA(){
          this.truth.a = this.truth.a+1;
        }
      },
      thoughts:{
        sum(){
          return this.truth.a + this.truth.b;
        }
      }
...

at this point, we can access sum like so:

	// ./my-component.js
...

	let localTruth = source.getTruth(['sum', 'a', 'b'], this)
	// localTruth.a is 1
	// localTruth.b is 2
	// localTruth.sum is 3
	if( localTruth.sum == (localTruth.a + localTruth.b) ){
		console.log('Ethos is legit.')
	}

...
	

but if we changed truth.a…

	// ./my-component.js
...

	source.writers.addOneToA()
	// localTruth.a is 2
	// localTruth.b is 2
	// localTruth.sum is 4

	if( localTruth.sum == (localTruth.a + localTruth.b) ){
		console.log('Redux who?')
	}

...

What’s this?

this for thoughts is the same as this for writers

• this.truth is your Source’s truth property.
  • It’s not suggested that you directly mutate truth from thoughts
• this.writers are your Source’s writers.
• this.runners are your Source’s runners.
• this.write is your Source’s write method.
• this.run is your Source’s run method.

Founder Function

In an Ethos Source, the founder function is a function that is instantly invoked once the source is built. It can be used to initialize a lot of source functionality an avoid contaminating your view layer with data logic.

Example:

...
      truth:{...},
      writers:{...},
		runners:{...},
      thoughts:{...},
		founder(){
			this.runners.authenticateUser();
			this.runners.openSockets();
		}
...

What’s this?

this for the founder function is the same as this for writers

• this.truth is your Source’s truth property.
  • It’s not suggested that you directly mutate truth from the founder function.
• this.writers are your Source’s writers.
• this.runners are your Source’s runners.
• this.write is your Source’s write method.
• this.run is your Source’s run method.

Children

To organize your sources, Ethos has children. Each child is its own independent source.

Child sources are defined like so:

import {
	Source,
} from 'ethos'

const source = {
		truth:{...},
		writers:{...},

		children:{
		// children are named by the property they are nested under
			users:{ // a source just for your users
				truth:{
					currentUser:{
						email:'',
						firstname:'',
						lastname:'',
						id:''
					}
				},
				thoughts:{
					fullName(){
						let user = this.truth.currentUser;
						return user.firstname + user.lastname;
					}
				},
				children:{ // nested children
					friends:{...}
				}
			}
		}

	}

export default new Source(source);

Access children on a source like so:

	let userSource = source.child('users')
	let userTruth = userSource.getTruth(['currentUser'], this)

Access nested children one of two ways:

1. chaining child methods

source.child('users').child('friends')

2. Query string

source.child('users.friends')

Runners, writers, thoughts, watchers and the founder function all have additional properties on this to access parent and child sources.

• this.child() is the source’s child method, same as above.
• this.parent is the source’s parent source.
• this.origin is the source’s origin source ( the one directly constructed with new Source)