cache-component

Cached bel components. Makes rendering elements very fast™. Analogous to React's .shouldComponentUpdate() method, but only using native DOM methods.

Runs a _render function whenever arguments changed according to an _update function. If the _update function determines an update is needed, a newly _rendered bel element is returned. If an update is not needed, a _proxy element is returned instead.

Features

• makes rendering elements very fast™
• implemented in only a few lines
• only uses native DOM methods
• Class based components, which offer a great place to store methods for re-use.

Usage

// Implementer API
var CacheComponent = require('cache-component')
var html = require('bel')

function CachedButton () {
  if (!(this instanceof CachedButton)) return new CachedButton()
  this._color = null
  CacheComponent.call(this)
}
CachedButton.prototype = Object.create(CacheComponent.prototype)

CachedButton.prototype._render = function (color) {
  this._color = color
  return html`
    <button style="background-color: ${color}">
      Click Me
    </button>
  `
}

// Override default shallow compare _update function
CachedButton.prototype._update = function (newColor) {
  return newColor !== this._color
}

var element = CachedButton()

let el = element('red') // creates new element
let el = element('red') // returns cached element (proxy)
let el = element('blue') // creates new element

// Consumer API
var CachedButton = require('./cached-button.js')
var cachedButton = CachedButton()
document.body.appendChild(cachedButton.render('green'))

API

CacheComponent.prototype()

Inheritable CachedComponent prototype. Should be inherited from using CacheComponent.call(this) and prototype = Object.create(CacheComponent.prototype).

Internal properties are:

• this._proxy: proxy element that's returned on subsequent render() calls that don't pass the ._update() check.
• this._isProxied: used to keep track if the proxy element has been created or not.
• this._element: rendered element that should be returned from the ._render() call.
• this._hasWindow: boolean if window exists. Can be used to create elements that render both in the browser and in Node.
• this._args: a reference to the arguments array that was used during the last _render() call.

CacheComponent.prototype._render([arguments])

Must be implemented. Render an HTML node with arguments. The Node that's returned is cached as this._element. Only called on first render and whenever you return true from prototype._update(). You must return a DOM node from this function on every call.

CacheComponent.prototype._update(newArgs, oldArgs)

Return a boolean to determine if prototype._render() should be called. Not called on the first render. Defaults to the following shallow compare function:

CacheElement.prototype._update = function (newArgs, oldArgs) {
  var length = newArgs.length
  if (length !== oldArgs.length) return true
  for (var i = 0; i < length; i++) {
    if (newArgs[i] !== oldArgs[i]) return true
  }
  return false
}

Installation

$ npm install cache-component

FAQ

Where does this run?

Make sure you're running a diffing engine that checks for .isSameNode(), if it doesn't you'll end up with super weird results because proxy nodes will probably be rendered which is not what should happen. Probably make sure you're using morphdom or [nanomorph][nm]. Seriously.

What's a proxy node?

It's a node that overloads Node.isSameNode() to compare it to another node. This is needed because a given DOM node can only exist in one DOM tree at the time, so we need a way to reference mounted nodes in the tree without actually using them. Hence the proxy pattern, and the recently added support for it in certain diffing engines:

var html = require('bel')

var el1 = html`<div>pink is the best</div>`
var el2 = html`<div>blue is the best</div>`

// let's proxy el1
var proxy = html`<div></div>`
proxy.isSameNode = function (targetNode) {
  return (targetNode === el1)
}

el1.isSameNode(el1)   // true
el1.isSameNode(el2)   // false
proxy.isSameNode(el1) // true
proxy.isSameNode(el2) // false

How does it work?

Morphdom is a diffing engine that diffs real DOM trees. It runs a series of checks between nodes to see if they should either be replaced, removed, updated or reordered. This is done using a series of property checks on the nodes.

Since v2.1.0 morphdom also runs Node.isSameNode(otherNode). This allows us to override the function and replace it with a custom function that proxies an existing node. Check out the code to see how it works. The result is that if every element in our tree uses cache-component, only elements that have changed will be recomputed and rerendered making things very fast.

nanomorph, which saw first use in choo 5, has supported isSameNode since it's conception.

What's the exact difference between cache-element and nanocomponent?

• cache-component returns a proxy node if the arguments were the same. If arguments change, it'll rerender and return a new node.
• nanocomponent will render a new node initially and always return a proxy node on subsequent calls to prototype.render. This means the component is responsible for mutating any internal changes. It also listens for the node to be unmounted from the DOM so it can clean up internal references, making it more expensive to use.

License

MIT