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Awesome Open Source


Smooth Router

A custom React router that leverages the Web Animations API and CSS animations.

Check out the demo!

Smoothr Logo


  • [x] Built with animating route transitions in mind
  • [x] Use the Web Animations API or CSS classes to animate
  • [x] Route and animate multiple sections of the page
  • [x] Hash Routing
  • [x] Minimal Polyfilling necessary (Just Object.assign(), Promise and possibly Element.animate(), for IE11 and newer)


In my experience of using animations with React Router and other Single Page App routing solutions, the work to add animation transitions on changing routes was a lot more complicated than just regular routing. I also was inspired by the Web Animations API and decided to create my own flavor of a Router, one that treats animations as first class citizens.

Anyway, thanks for checking this library out. If you end up using Smoothr in production, let me know and I'll add a link here in the README.

May your single page routing animations be smoother, with Smoothr... (pardon the cheesyness)

Getting Started



$ npm install --save smoothr


$ yarn add smoothr

Minimal Example Usage

import React from 'react';
import ReactDOM from 'react-dom';

// Bring in the Smoothr components
import { Smoothr, SmoothRoutes, Route, Link } from 'smoothr';

const Page = props => <section>{props.message}</section>;

const App = () => (
      {/* Link is our wrapper around anchors for Smoothr navigation  */}
      <Link href="/">Home</Link>
      <Link href="/anotherpage">Another Page</Link>
          // Use the Web Animations API, first argument of Element.animate()
          animationIn={[{ opacity: 0 }, { opacity: 1 }]}
          animationOut={[{ opacity: 1 }, { opacity: 0 }]}
          // and the second argument of Element.animate()
            duration: 750,
            easing: 'ease-in-out'
          // Any other props will be passed to `component`
          message="Welcome to the homepage!"
          // Use CSS classes for animating
          message="Welcome to the other page!"
          // The `notFound` prop designates a route, path, and component for 404 page
          message="404 Error!"

For a more complete example, check out the demo and its source code. If you want to play around with this example, see the setup instructions in the Contributing section.

API Documentation



The <Smoothr> component just needs to be used up the tree of any <Link>s or <SmoothRoutes>. I recommend having it at the top level of your Single Page App. <Smoothr> props are the top-level configuration for all routing.

Available props: (* indicates a required prop)

  • beforeAnimation - (function) - This method is the entry point into knowing what's going on with the Smoothr routing. It is used in a Promise which will resolve before starting the animation to ensure the completion of any asynchonous state changes before animating. Use it to change local state in order to conditionally set the upcoming animation. Example:
beforeAnimation = ({
  // Url's are the exact urls
  // Routes are the original matching routes, as set in the <Route /> components
  // If the user nagivated with the "back" button in the browser (boolean)
}) => {
  // Set local state in order to configure upcoming <Route> animation props
  // ...
  • onAnimationStart - (function) - This function will run right before the animation begins. Use it to imperitively kick off transition animations. If you want to kick off an animation based on incoming or outgoing routes, use beforeAnimation to set some state, and then use that state in this method.

  • onAnimationEnd - (function) - This takes place after the animation is finished. Tell your app that it's done animating, reset some configuration saved in state, or do something else. There are no arguments passed.

  • originPath - (string) - The path after the domain to the origin of this single page app. This includes the beginning backslash, but not the trailing backslash. This will be set once and cannot be updated. All of the <Link> href properties will be relative to that origin path. For hash routing, set this to "/#" or something else ending with a hash (#), and that's it! Example: "/smoothr-app", and <Link href="/page1" /> will link to "/smoothr-app/page1". This defaults to an empty string, which signifies the document root.



Imagine <SmoothRoutes> as a regular DOM element that changes when the url changes. Its children MUST be <Route> components. You can use as many of these on the page as you want. Often you'll want to wrap each <SmoothRoutes> component in a wrapper DOM element with some CSS rules or a MutationObserver to set its size.

Available props:

Each of these props are identical to their <Route> counterparts. They will be applied to all routes if set at the <SmoothRoutes> level, but if a <Route> has an animation prop, the logic will favor the props set on the <Route> at transition time.



Most of the actual animation configuration takes place on the <Route> level. Animations are set by the props of the <Route> that is being transitioned in. The reverseAnimation prop equivalents take precedence when the user nagivates back with the "back" button in their browser, but aren't required.

Available props: (* indicates a required prop)

  • component* - (React Component) - The component that you want to be rendered when the URL matches a given path.
  • path* - (string) - When the url matches the path of your <Route>, it will render to the page. Variabled routes are supported, and can be indicated with a colon (:). The value of that variable will be passed down as a prop by the name in the path to the rendered component. Example of using path with variables:
<Route path="/users/:id" component={UsersPage} />

// If the url is "/users/12345", the following will be rendered:
<UsersPage id="12345">
  • pathResolve - (function) - Use this function to validate and modify the variables passed when this <Route> is navigated to. The return value must match the pattern of the path. If it doesn't, the notFound path will be used. This will only work if the path component has variables. Example, which can by tested on the live demo:
  pathResolve={({red, green, blue}) => {
    // Ensure they're all numeric
    if(isNaN(red) || isNaN(green) || isNaN(blue)) {
      // Return anything not matching the `path` pattern to trigger a 404
      return false; 
    // Make sure they're all valid RGB values
    red = Math.min(Math.abs(parseInt(red)), 255);
    green = Math.min(Math.abs(parseInt(green)), 255);
    blue = Math.min(Math.abs(parseInt(blue)), 255);
    // Return the resolved url
    return `/color/${red}/${green}/${blue}`;
  // ...
  • animationIn - (Element.animate() keyframes argument, or string indicating className) - The value of this prop corresponds to the first argument of the Element.animate() method, or a css class name, which will be applied to the <Route> DOM element during the duration of the animation. If this isn't passed, then no animation will occur, but be aware that the incoming <Route> won't show up until the duration ends, as set in the animationOpts prop of either the <SmoothRoutes> or <Route> component.
  • animationOut - (Element.animate() keyframes argument, or string indicating className) - Similiar to animationIn, but is applied to the outgoing <Route>
  • animationOpts - (Element.animate() options argument) - This corresponds to the second argument of the Element.animate() method. These options are applied to both the incoming and outgoing <Route>s during transition. If using a CSS class transition, then any other options passed to an object besides duration will be ignored. If this prop is not set, the animation duration will default to 0.

NOTE: There are a couple of nuances to how Smoothr uses the options argument of Element.animate().

  1. fill is always set to forwards
  2. iterations cannot be set to Infinity.



Links are wrappers around anchor (<a>) tags. The library adds the prop data-smoothr-current-link="true" when the href matches the current URL, and the data-smoothr-visited-link property to simulate the css :visited rule. When styling, use these data-attributes in your css rules, like so

a[data-smoothr-current-link="true"] {
  /* some style to show the currently opened link here */

a[data-smoothr-visited-link="true"] {
  /* some style to show a visited link here */

Available props: (* indicates a required prop)

  • href* - (string) - Same as anchor tag
  • onClick - (function) - This is self-explanatory
  • fuzzyCurrent - (No type, just set the prop) - If is prop is set, the data-smoothr-current-link property will be added to the link if the route matches the current variabled route. By default, only exact url matches will have the data-smoothr-current-link property added.
  • fuzzyVisited - (No type, just set the prop) - Similiar to the fuzzyCurrent prop, but related to visited links. If the user visits a Route with a matching variable pattern, the data-smoothr-visited-link property will be added.
  • Any other props that are set will be passed down to the rendered anchor tag.

To do list before version 1.0.0:

  • [x] Release initial build to NPM
  • [x] Add ability to validate and mask URL variables on navigation
  • [x] Test on Chrome, Firefox, Safari, Edge and IE11.
  • [x] Handle visited links and current links better
  • [x] Remove glitchiness around interrupted animations
  • [x] Add hash routing
  • [x] General cleanup
  • [ ] Test on Edge and IE11.
  • [ ] Add prop checks with PropTypes
  • [ ] Test app in Preact/add Preact support
  • [ ] Remove need to polyfill Object.assign and possibly Promise
  • [ ] Optimization
  • [ ] Add more animations to the demo page


I plan on maintaining this library. For bugs and enhancements, just add an issue and/or send pull request my way, and I'll review it! I'm definitely open to improvements.


You can set up your development environment and use the example app as a test app by running the following commands:

$ git clone
$ cd smoothr
$ yarn install
$ yarn build
$ cd example
$ yarn install
$ yarn start

and then when you want to reload the package, from the smoothr directory

$ yarn build

It may take a while to download the dev dependencies.


Nate Adams

💻 🎨 📖 💡 🤔 📦

Morgan Kartchner

🤔 🚇


This project is licensed under the MIT License - see the LICENSE file for details


  • Big thanks to Morgan Kartchner for the mentoring and contributions to the Dayzed library, which I used as a guide in setting up this lib.
  • The folks at MDN for writing up the Web Animations API documentation
  • You, for checking out this library! Thanks!
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