Add <Subscriber quiet>

Fixes #41

Author: Michael Jackson

modules/Subscriber.js

@@ -10,22 +10,27 @@ class Subscriber extends React.Component {
   static propTypes = {
     channel: PropTypes.string.isRequired,
     children: PropTypes.func,
+    quiet: PropTypes.bool
+  }
+
+  static defaultProps = {
+    quiet: false
   }
 
   static contextTypes = {
     broadcasts: PropTypes.object
   }
 
   state = {
-    value: null
+    value: undefined
   }
 
   getBroadcast() {
     const broadcasts = this.context.broadcasts || {}
     const broadcast = broadcasts[this.props.channel]
 
     invariant(
-      broadcast,
+      this.props.quiet || broadcast,
       '<Subscriber channel="%s"> must be rendered in the context of a <Broadcast channel="%s">',
       this.props.channel,
       this.props.channel
@@ -35,19 +40,27 @@ class Subscriber extends React.Component {
   }
 
   componentWillMount() {
-    this.setState({
-      value: this.getBroadcast().getState()
-    })
+    const broadcast = this.getBroadcast()
+
+    if (broadcast) {
+      this.setState({
+        value: broadcast.getState()
+      })
+    }
   }
 
   componentDidMount() {
-    this.unsubscribe = this.getBroadcast().subscribe(value => {
-      this.setState({ value })
-    })
+    const broadcast = this.getBroadcast()
+
+    if (broadcast) {
+      this.unsubscribe = broadcast.subscribe(value => {
+        this.setState({ value })
+      })
+    }
   }
 
   componentWillUnmount() {
-    this.unsubscribe()
+    if (this.unsubscribe) this.unsubscribe()
   }
 
   render() {

modules/__tests__/Subscriber-test.js

@@ -0,0 +1,19 @@
+import React from "react"
+import ReactDOMServer from "react-dom/server"
+import Subscriber from "../Subscriber"
+
+describe("A <Subscriber>", () => {
+  it("throws an invariant when it is not rendered in the context of a <Broadcast>", () => {
+    expect(() => {
+      ReactDOMServer.renderToStaticMarkup(<Subscriber channel="cupcakes" />)
+    }).toThrow()
+  })
+
+  describe("with quiet=true", () => {
+    it("does not throw when it is not rendered in the context of a <Broadcast>", () => {
+      expect(() => {
+        ReactDOMServer.renderToStaticMarkup(<Subscriber quiet channel="cupcakes" />)
+      }).not.toThrow()
+    })
+  })
+})