React integration

Evt let you work with events in react without having to worry about cleaning up afterward.

Checkout this quick example:

import { useState } from "react";
import { Evt } from "evt";
import { useEvt } from "evt/hooks";
const evtTick = Evt.create();
setInterval(()=>, 1000);
function App(){
const [count, setCount]= useState(0);
useEvt(ctx=> {
evtTick.attach(ctx, ()=> setCount(count+1));
return <h1>tick count: {count}</h1>;

Run it

The core idea is to always use the cts to attach handlers. This will enable EVT to detach/reload handlers when they need to be namely when the component is unmounted or a value used in a handler has changed.

Custom hooks

Evt let enables you to create powerful custom hooks. Here are some examples:

Custom hook that gives the innerWith of the window

import { Evt } from "evt";
import { useEvt, useStatefulEvt } from "evt/hooks";
export function useWindowInnerWidth() {
const evtInnerWidth = useEvt(ctx =>
Evt.from(ctx, window, "resize")
.pipe(() => [window.innerWidth])
return { "windowInnerWidth": evtInnerWidth.state };

Usage ( you'll have to resize the window to see the text change )

import { useWindowInnerWidth } from "app/utils/hooks/useWindowInnerWidth.ts";
export function MyComponent(){
const { windowInnerWidth } = useWindowInnerWidth();
return <h1>window.innerWidth is: {windowInnerWidth}px</h1>;

This example will only work with EVT v2.0

Custom hooks that enable to toogle dark mode

This hook use for default value the OS default (true if the user have dark mode enabled system whild) and persist de result value in local storage.

import { useState } from "react";
import { Evt } from "evt";
import { useEvt } from "evt/hooks";
const key = "isDarkModeEnabled_dXddOm";
const evtIsDarkModeEnabled = Evt.create(
(() => {
const value = localStorage.getItem(key);
return value === null ? null : value === "true";
})() ??
window.matchMedia("(prefers-color-scheme: dark)").matches
isDarkModeEnabled => localStorage.setItem(
key, isDarkModeEnabled ? "true" : "false"
export function useIsDarkModeEnabled(): {
isDarkModeEnabled: boolean;
setIsDarkModeEnabled(params: { isDarkModeEnabled: boolean; }): void;
} {
const [isDarkModeEnabled, setIsDarkModeEnabled] =
useEvt(ctx =>
.toStateless(ctx) //We use .toStateless() to avoid calling setIsDarkModeEnabled on first render
return {
"setIsDarkModeEnabled": ({ isDarkModeEnabled }) =>
evtIsDarkModeEnabled.state = isDarkModeEnabled


You can use this react-hooks/exhaustive-deps setting to be warned if you forget a dependency:

//package.json (if you use create-react-app otherwise use .eslintrc.js)
"eslintConfig": {
"extends": [
"rules": {
"react-hooks/rules-of-hooks": "error",
"react-hooks/exhaustive-deps": [
"additionalHooks": "(useEvt)"

Mini "Hello World" project Example

Live code

Just a basic example to demonstrate how to use the Hooks.

Comprehensive example: A TODO list app

This example is meant to show how EVT can help you build fully reactive UI that can be synced in real time across devices.

It also provides gidelines on how to optimize as much as possible the performance of the UI.

NOTE: The request delay are simulated to show how the UI would handle slow network.

Live code / GitHub repo