User Events

Part of the power that Javascript gives us when creating apps in the browser is the ability to listen and take action when a user interacts with our app.

To listen for these occurrences, we need a way to run code AFTER something happens. For this, all HTMLElement objects inherit from EventTarget which has an addEventListener function which allows us to add callback functions to be run once a particular event "fires".

Some Terminology

• Target - An element or object on which events can be listened for or triggered
• Trigger/Dispatch - When all the handlers for a named event need to be run, this usually happens through native WebAPIs

Listening for Clicks

The addEventListener function takes two arguments:

• Then name of the event that should be listened for
• A callback to be run when the event fires

So, let's make the button below trigger a browser alert:

var alertButton = document.querySelector('.alert-button');

alertButton.addEventListener('click', () => {
  alert(`button clicked`);
});

Other Events

While the click event is the most common event that we will listen for, there are other events that we may want to listen for:

• input - When any text input is put into or removed from an input element or parent elements
• change - When text in an input has changed and a user has left focus
• mouseover - When the user mouse enters the current element or any of its children
• mouseenter - When the user mouse enters the current element but does not trigger again until after leaving the entire element
• scroll when the scroll of the current element has been scrolled - Useful for parallax style scroll effects