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A controller for Backbone, linking Models to Views
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README.md

For a quick example of how myelin works, check here.

Myelin automates the linking of your HTML elements to your Backbone Models, through your Backbone Views. All you need to do is use myelin.View instead of Backbone.View, and declare a 'sync' attribute on your view, like this:

class MyView extends myelin.View
    sync:
        user: 'input[name=user]'
        message: '#message'

Then, myelin will link a form like this:

<form id="myForm">
    <input name="user">
    <span id="message"></span>
</form>

to a model like this:

model = new Backbone.Model message: "Hello, world!"

using a view like this:

view = new MyView {el: '#myForm', model}

Any changes to the "user" input field will update the "user" attribute on the model, and any change to the "message" attribute of the model will be reflected in the message span.

Quick Tip

The {attr: [name=attr]} sync pattern is so common that you can use the shortcut {attr: true}. It means the same thing. So, for example, the above model could be reduced to

class MyView extends myelin.View
    sync:
        user: true
        message: '#message'

Quickly now

If you're the impatient type, you might want to jump directly to some examples, or perhaps the annotated source.

How to Use

Myelin is used by creating myelin Views with a sync property that controls how objects are linked. Before linking can be done, views must also have both an el property and a model property set. You are welcome to set these any time after view creation and change them on the fly, so long as you call view.link() any time you change el or model.

You can even change the sync attribute, although it's not quite so easy. If you update the sync object, you'll have to call view.updateAxons before the changes take effect.

The sync property describes links between forms and models in a number of formats. Before we go over the different formats for links, you must understand how links works. Each link consists of three parts: an attribute, a selector, and a handler.

Attributes

Attributes are the most simple component of a link. They are simply a string naming the attribute on the model that you want to sync your data to. If a string isn't quite flexible enough, you can also provide a function that takes the DOM elements being linked and returns the attribute to sync to at event-time. If the attribute is omitted then a fallback function (that depends upon the selector) will be used. Because attribute functions depend upon the elements being synced, if the attribute is a function then the selector must be provided as a string.

The fallback function returns the "name" attribute of the elements being linked. For example, if you link create a link to an element <input name="test"> and you don't provide an attribute, the element will be synced to the test attribute.

Selectors

Selectors are simply a jQuery selector used to select the elements being linked. The actual elements will be selected as late as possible, in the context of the view's el. Thus, if you dynamically add or remove elements that match the selector to the view, the elements will automatically be linked.

If you want to bind to the actual view el (instead of the view's children), use the special 'this' selector.

You may also provide a function to determine the selector; this function will be called with the attribute of the link. If the selector is a function then an attribute must be provided.

The fallback function selects elements with the same name as the attribute. For example, if you create a link to the attribute 'user', then the selector name="user" will be linked.

Handlers

Handlers bridge the gaps between DOM elements and model attributes. At their core, handlers preform four actions:

  • get data from an element
  • clean element data for a model
  • render model data for an element
  • set rendered data on an element

The also control the linking in three ways:

  • domEvent
    • controls the DOM event that triggers syncing
    • if falsy then the model will not respond to DOM changes
    • can be a function which will be passed the elements being synced
  • modelEvent
    • controls the model event that triggers syncing
    • if falsy then the DOM will not respond to model changes
    • can be a function which will be passed the attribute being synced
  • preventDefault
    • controls whether or not the default DOM event is prevented

Handlers can always be left out of a link, in which case they will be inferred from the elements being bound using myelin.handlerMap and myelin.defaultHandler.

A handful of handlers come built in to Myelin. You can provide your own handlers to customize data manipulation. The built in handlers are as follows:

Handler

The default handler is used for divs, spans, and other elements that don't take user input. It works as follows:

  • get accesses inner html
  • set sets inner html
  • clean performs no action
  • render performs no action
  • domEvent is false, as these elements never change on their own
  • modelEvent returns "change:#{attribute}"
  • preventDefault is false

Input

A Handler used for most inputs. gets and sets using jQuery's .val(). domEvent is "change", meaning the model will be synced whenever a "change" event is fired. Used by default for input and select elements.

ImmediateInput

An Input that syncs on "keyup" instead of "change". Used by default for textareas.

Password

A handler that cleans passwords. The handler will salt and hash the password with the bcrypt module, if bcrypt is available. This is disconcerting to the user, as it causes the password to appear to change length, but the alternative is storing plaintext passwords on your models. This is fine, but please don't store plaintext passwords anywhere permanent.

You should think carefully about how you store your passwords, and override myelin.Password to reflect your usage scenarios.

myelin.Password is not intended for production use.

Button

Button elements don't visually display their data, but rather store it using jQuery.data on the 'value' field. Buttons push stored data on the click event.

Submit

Like Button, but prevents the default DOM event from being fired.

Checkbox

An Input handler that handles checking and unchecking its element. Note that render and clean will both convert their values to Booleans.

Radio

An Input handler that handles selecting the correct radio element. The selector should match a whole set of radio buttons. get will return the value of the checked button, and set will ensure that only the button with the matching value is checked.

Specifying Links

In order to specify a link, you must specify the attribute, handler, and selector that you would like to use. Any of these can be left out, but if you leave out the attribute then you have to provide a selector, and visa versa.

Links are specified on the sync attribute of a view. Usually, sync is an object, but it can also be a single item or a list of items: see the shorthand section below.

The Sync object

Sync objects are given in the form

attribute: specification

Where specification can take the following forms:

  • false
    • if the specification is false then the attribute will be ignored. This allows specification functions to essentially say 'never mind'.
  • true
    • if the specification is true then a link will be made where both the handler and selector are omitted.
  • array
    • given {attr: [selector1, selector2]}, the links attr: selector1 and attr: selector2 will be created.
  • function
    • the function will be resolved with the view as it's context and the attribute as a parameter. The result will be parsed recursively.
  • handler class
    • a link will be made between the attribute and an instantiated version of the handler class. The selector will be omitted.
  • handler instance
    • a link will be made between the attribute and the handler. The selector will be omitted.
  • string
    • treated as a selector. A link will be made with the handler omitted.
  • object
    • an object can be passed with 'handler', 'selector', and optionally 'event' properties, which will all be used to make the link.

Convenient Events

A selector string can be given in the form "event selector" (a jQuery event separated from the selector by whitespace). In this case, the event will be split off from the selector and will override handler.domEvent. For example,

{name: "keyup [name=firstname]"}

will create a link between the attribute 'name' and the selector '[name=firstname]'. An Input handler will be used, but the handler will listen for the 'keyup' event instead of the usual 'change' event.

You can also provide an 'event' property in a specification as follows:

{name: {selector: "[name=firstname]", event: "keyup"}}

for the same effect. Recognized events are whitelisted in myelin.events.

Shorthand

If you want to be even more terse, sync doesn't need to be an object. It can also be an array or a string.

sync: ["first_name", "last_name"]

is identical to

sync: {first_name: true, last_name: true}

which, in turn, is the same as

sync: {first_name: "[name=first_name]", last_name: "[name=last_name]"}

assuming you didn't override the fallback selector function.

You can also provide Axon instances directly, though that's only recommended for advanced users.

Under the Hood

Under the hood, myelin uses a class called Axon to manage links. An axon takes four parameters in an object in the constructor. They are: * attribute * selector * handler * event

event, if given, overrides handler.domEvent.

Configuration

Myelin can be configured in a variety of ways:

Changing Handler assignment

If you want to change the default handlers, override myelin.handlerMap. myelin.handlerMap is a list of (selector, handler) two-tuples that determine which handler is used for which selector (if no handler is specified). Handlers are matched from top to bottom, and if no match is found then myelin.defaultHandler is used instead.

Changing the fallback attribute

If an attribute is omitted, it is determined using the Axon.attribute function, which takes the linked elements and returns the model attribute to sync to. To change this behavior, override Axon.attribute.

Changing the fallback selector

If a selector is omitted, it is determined using the Axon.selector function, which takes the model attribute and returns a selector. To change this behavior, override Axon.selector.

Changing Axon

If you find yourself overriding a number of Axon functions, it may be easier to subclass Axon and simply tell myelin to use a different Axon class. To do this, simply set myelin.axon to your Axon class. Note that your custom axon must be a child of myelin.Axon if you want things to work properly.

Resources

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