react-start-transition

React 18 startTransition polyfill

With the upcoming startTransition primitive coming to React 18, I decided to create a lil polyfill to help developers transition to the new API and get some perf improvements already.

This lib won't have the same perf impact as the native startTransition will since it doesn't have access to React internals (more info here) but it will use what's best available and only run the tasks when the browser is not busy doing other more critical stuff.

A combination of isInputPending and requestIdleCallback browser API's will be used for that.

Install

$ yarn add react-start-transition

Usage

import * as React from "react";
import { useState } from "react";
import { useTransition } from 'react-start-transition'

const App = () => {
  const [isPending, startTransition] = useTransition();
  const [inputValue, setInputValue] = useState(5);
  const onChange = (value: number) => {
    startTransition(() => setInputValue(value));
  };
  
  return (
    <div>
      <Slider defaultValue={inputValue} onChange={onChange} />
      <div>{isPending && 'loading...'}</div>
      <div>{inputValue}</div>
    </div>
  );
};

isPending

Notice that when you use the isPending from

const [isPending, startTransition] = useTransition();

it will be coupled to the task that you run within the startTransition and will done whenever that task get ran by the internal scheduler.