why push notification not showing in chrome code example

Example: chrome extension notification not showing

If you are using Mac and Chrome 59+, it might be because the MacOS native notification is disabled for Chrome. Here's two possible solutions:

Solution 1
Open Chrome > Go chrome://flags > Search Enable native notifications > Change it to Disabled > Relaunch Chrome

Solution 2
Go to MacOS System Preferences > Notifications > Turn on Notifications for Banners/Alerts as shown here (likely previously it's Off)