Subscriber must render in proper context

Also, broadcast.subscribe no longer emits on the same tick, but this is
an implementation detail.

Fixes #6

Author: mjackson

modules/Broadcast.js

@@ -5,20 +5,25 @@ const createBroadcast = (initialValue) => {
   let listeners = []
   let currentValue = initialValue
 
+  const getValue = () =>
+    currentValue
+
+  const setValue = (value) => {
+    currentValue = value
+    listeners.forEach(listener => listener(currentValue))
+  }
+
+  const subscribe = (listener) => {
+    listeners.push(listener)
+
+    return () =>
+      listeners = listeners.filter(item => item !== listener)
+  }
+
   return {
-    publish(value) {
-      currentValue = value
-      listeners.forEach(listener => listener(currentValue))
-    },
-    subscribe(listener) {
-      listeners.push(listener)
-
-      // Publish to this subscriber once immediately.
-      listener(currentValue)
-
-      return () =>
-        listeners = listeners.filter(item => item !== listener)
-    }
+    getValue,
+    setValue,
+    subscribe
   }
 }
 
@@ -48,7 +53,7 @@ class Broadcast extends React.Component {
 
     return {
       ...broadcasts,
-      [channel]: this.broadcast.subscribe
+      [channel]: this.broadcast
     }
   }
 
@@ -65,7 +70,7 @@ class Broadcast extends React.Component {
     )
 
     if (this.props.value !== nextProps.value)
-      this.broadcast.publish(nextProps.value)
+      this.broadcast.setValue(nextProps.value)
   }
 
   render() {

modules/Subscriber.js

@@ -14,29 +14,35 @@ class Subscriber extends React.Component {
     value: null
   }
 
-  componentWillMount() {
-    const { channel } = this.props
+  getBroadcast() {
+    return this.context.broadcasts[this.props.channel]
+  }
 
-    if (this.context.broadcasts) {
-      const subscribe = this.context.broadcasts[channel]
+  componentWillMount() {
+    const broadcast = this.getBroadcast()
+
+    invariant(
+      broadcast,
+      '<Subscriber channel="%s"> must be rendered in the context of a <Broadcast channel="%s">',
+      this.props.channel,
+      this.props.channel
+    )
+
+    this.setState({
+      value: broadcast.getValue()
+    })
+  }
 
-      invariant(
-        typeof subscribe === 'function',
-        '<Subscriber channel="%s"> must be rendered in the context of a <Broadcast channel="%s">',
-        channel,
-        channel
-      )
+  componentDidMount() {
+    const broadcast = this.getBroadcast()
 
-      this.unsubscribe = subscribe(value => {
-        // This function will be called once immediately.
-        this.setState({ value })
-      })
-    }
+    this.unsubscribe = broadcast.subscribe(value => {
+      this.setState({ value })
+    })
   }
 
   componentWillUnmount() {
-    if (this.unsubscribe)
-      this.unsubscribe()
+    this.unsubscribe()
   }
 
   render() {