Developer console
One of the key element in JavaScript development is browser console, also known as developer toolbar. We are human and we will quite high likely make many errors. Console is helping us to identify where the problem is.
Most of the browsers opens the console either SHIFT + CTRL + I or F12 shortcuts. Although these days most of them have the same functionalities, we prefer to use Google Chrome. We will explaing Google Chrome but you have the same features on others as well.
Here are tabs that you can use in developer toolbars
Elements
Recorder
Console
Network
Performance
Memory