--- a/client/src/components/Clock.js	Mon Jun 12 11:39:47 2017 +0200
+++ b/client/src/components/Clock.js	Mon Jun 12 18:09:13 2017 +0200
@@ -6,13 +6,20 @@
 
   state = {
     time: moment().format('H:mm:ss'),
+    intervalID: null
   }
 
   componentDidMount() {
-    setInterval(() => {
+    const intervalID = setInterval(() => {
       const time = moment().format('H:mm:ss');
       this.setState({ time });
     }, 1000);
+
+    this.setState({ intervalID });
+  }
+
+  componentWillUnmount() {
+    clearInterval(this.state.intervalID);
   }
 
   render() {