Performance optimisation

Add shouldComponentUpdate for LogMonitorEntry to make it performant
when triggering events rapidly such as onKeyDown.

src/react/LogMonitor.js

@@ -38,6 +38,7 @@ export default class LogMonitor extends Component {
     if (typeof window !== 'undefined') {
       window.addEventListener('keydown', ::this.handleKeyPress);
     }
+    this.handleToggleAction = this.handleToggleAction.bind(this);
   }
 
   static propTypes = {
@@ -173,7 +174,7 @@ export default class LogMonitor extends Component {
                          previousState={previousState}
                          collapsed={skippedActions[i]}
                          error={error}
-                         onActionClick={::this.handleToggleAction} />
+                         onActionClick={this.handleToggleAction} />
       );
     }
 

src/react/LogMonitorEntry.js

@@ -1,6 +1,7 @@
 import React, { PropTypes, Component } from 'react';
 import JSONTree from 'react-json-tree';
 import LogMonitorEntryAction from './LogMonitorEntryAction';
+import shallowEqual from '../utils/shallowEqual';
 
 const styles = {
   entry: {
@@ -23,6 +24,10 @@ export default class LogMonitorEntry extends Component {
     collapsed: PropTypes.bool
   };
 
+  shouldComponentUpdate(nextProps) {
+    return !shallowEqual(this.props, nextProps);
+  }
+
   printState(state, error) {
     let errorText = error;
     if (!errorText) {

src/utils/shallowEqual.js

@@ -0,0 +1,27 @@
+export default function shallowEqual(objA, objB) {
+  if (objA === objB) {
+    return true;
+  }
+
+  if (typeof objA !== 'object' || objA === null ||
+      typeof objB !== 'object' || objB === null) {
+    return false;
+  }
+
+  const keysA = Object.keys(objA);
+  const keysB = Object.keys(objB);
+
+  if (keysA.length !== keysB.length) {
+    return false;
+  }
+
+  // Test for A's keys different from B.
+  const bHasOwnProperty = Object.prototype.hasOwnProperty.bind(objB);
+  for (let i = 0; i < keysA.length; i++) {
+    if (!bHasOwnProperty(keysA[i]) || objA[keysA[i]] !== objB[keysA[i]]) {
+      return false;
+    }
+  }
+
+  return true;
+}