choo components (#639)

* add components

* example: componentize header

* fix choo SSR

* example: componentize footer

* example: fix footer

* update component cache asserts

* componentize todos

* reorder example dir

* fix example tests

* fix dep check test

* Add garbage collection of unused components

* Apply args when calling identity

* update to new component preview

* update nanocomponent

* fix cache err name

* remove static methods from example

* restore app.emit() function

* public API tests

* offset component cache iteration by 2

* whitelist contents of component folder (#643)

* allow lru number arg

* fix lint typo

component/cache.js

@@ -0,0 +1,41 @@
+var assert = require('assert')
+var LRU = require('nanolru')
+
+module.exports = ChooComponentCache
+
+function ChooComponentCache (state, emit, lru) {
+  assert.ok(this instanceof ChooComponentCache, 'ChooComponentCache should be created with `new`')
+
+  assert.equal(typeof state, 'object', 'ChooComponentCache: state should be type object')
+  assert.equal(typeof emit, 'function', 'ChooComponentCache: emit should be type function')
+
+  if (typeof lru === 'number') this.cache = new LRU(lru)
+  else this.cache = lru || new LRU(100)
+  this.state = state
+  this.emit = emit
+}
+
+// Get & create component instances.
+ChooComponentCache.prototype.render = function (Component, id) {
+  assert.equal(typeof Component, 'function', 'ChooComponentCache.render: Component should be type function')
+  assert.ok(typeof id === 'string' || typeof id === 'number', 'ChooComponentCache.render: id should be type string or type number')
+
+  var el = this.cache.get(id)
+  if (!el) {
+    var args = []
+    for (var i = 2, len = arguments.length; i < len; i++) {
+      args.push(arguments[i])
+    }
+    args.unshift(Component, id, this.state, this.emit)
+    el = newCall.apply(newCall, args)
+    this.cache.set(id, el)
+  }
+
+  return el
+}
+
+// Because you can't call `new` and `.apply()` at the same time. This is a mad
+// hack, but hey it works so we gonna go for it. Whoop.
+function newCall (Cls) {
+  return new (Cls.bind.apply(Cls, arguments)) // eslint-disable-line
+}

component/index.js

@@ -0,0 +1 @@
+module.exports = require('nanocomponent')