What is Reactive State Management?

Reactive State is state that updates continuously in response to specific events and is Observable.

Lets develop a real world Typescript Stackblitz example using the Firefly Semantic Reactive Entity Store. We also have this on youtube in case you’d like to follow along there:

If doing this from scratch make sure to add Firefly Semantics Slice to the dependencies of the Stackblitz:

The entity store will be populated with Todo instances:

interface Todo {gid?: string;id?: string;complete: boolean;title: string;}

Each time we add a new Todo to the store, the store will respond reactively by updating the count observable tied to it.

The function used to observe the count updates looks like this:

function countSubscription(c) {
console.log(`The current Todo count is ${c}`);

And we observe the stores count Observable like this:

(c) => console.log(`Observed count of Todo entities ${c}`)

The Todo instances we will be adding are as follows:

const TODO1: Todo = {
id: TODO_ID_1,
complete: false,
title: 'You complete me!',
const TODO2: Todo = {
id: TODO_ID_2,
complete: true,
title: 'You completed me!',

Each time a Todo is added the count will update and we will see a logging notification. Initially this will be logged:

Todo entity count: 0

That logging statement is triggered when the our countSubscription() function is subscribed to the count Observable .

Lets add the first Todo :


We now see that Todo entity count: 1is logged.

Lets add the second one:


We now see that Todo entity count: 2is logged.

We can imagine this being used in for example a shopping cart where we want to update and display the number of items in the cart reactively as they are added.



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Ole Ersoy

Ole Ersoy

Founder of Firefly Semantics Corporation