![]() ![]() Note with arrow functions it is possible to wire up one-liner events. Then, attaching the event listeners to bring it to life. I’m using the body.appendChild() in the DOM API to add this new element. This will track changes in the text area and give you a word count right beneath it. Take all your reusable code and put in place the observer design pattern. addEventListener ( 'keyup', ( ) => blogObserver. To initialize the EventObserver do: class EventObserver ) const blogPost = document. The word count component will take this observer and bring it all together. └── broadcast: executes all events with bound dataĪfter I flesh out the observer pattern I’ll add a word count that uses it. ![]() ![]() ├── unsubscribe: removes observable events ├── subscribe: adds new observable events So, let’s get started.Ī high-level view of the pattern looks like this: EventObserver The new language features in ES6 make for some succinct code. This way you have a way knowing how each component is useful. I’ll use parts of ES6 that introduce syntactic sugar only, so it is portable with ES5 if need be.Īnd I’ll use Test-Driven-Development (TDD) to work on the pattern. Feel free to explore these topics on your own if you are not already familiar. Yes, there will be classes, arrow functions, and constants. I’ll use ECMAScript 6 to illustrate the pattern. It is a problem that comes up often when you have many elements that must be in sync. That is one-to-many, one-way, and event-driven data binding. ![]() It will help you solve a common problem you see in client-side scripting. In this article, I’d like to explore the observer design pattern. With this pattern, you can build reusable code that solves for your specific needs. This one-way data binding can be event driven. This is where the observer design pattern can help - it enables one-to-many data binding between elements. This leads into a lot of push-and-pull in the code to keep everything in sync. Say, for example, user input that you then project into one or many components. You need a way to update parts of a page in response to certain events, with the data these provide. In JavaScript, there is a problem that comes up often. ![]()
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