Add this function binds to Navbar constructor

src/components/Job/index.tsx

@@ -21,6 +21,7 @@ export default class Experience extends React.PureComponent<Props> {
       </div>
     )
   }
+
   private renderBullets() {
     return this.props.bullets.map((bullet, index) => (
       <li key={index}>{bullet}</li>

src/components/Navbar/index.tsx

@@ -14,6 +14,10 @@ class Navbar extends React.Component<{}, State> {
   constructor(props: {}) {
     super(props)
     this.state = { showMenu: !this.isMobile() }
+
+    this.toggleMenu = this.toggleMenu.bind(this)
+    this.renderButtons = this.renderButtons.bind(this)
+    this.closeMenu = this.closeMenu.bind(this)
   }
 
   public render() {