How to build your own React-Router with new React Context Api

Steven Koch
Apr 6, 2018 · 4 min read
Photo by Chris Barbalis on Unsplash

React Context is not something new for react.js developers, but it was something that was always used by the most courageous (React-Redux, React-Router, …), even in the documentation was itself discounted. However this has changed with the release of the new version of React 16.3 which came with an official version of a new API to work with context.

First I would like to apologize for this unpretentious article, it was written based on my latest experiments on the new version of React and the code you found here was extracted from it. React-Router is much more than what I’m presenting, but this example will explain how you can too develop something similar using the new context api.

Contexts

Contexts are a way to pass state from top to bottom (parent to grandchildren) without having to propagate these state to intermediate components (children).

New React Context API

The new React Context API has three main parts:

From dailyjs:

  • React.createContext which is passed the initial value (and optionally a fancy opt-out function that uses a bitmask). This returns an object with a Provider and a Consumer”
  • “The Provider component is used higher in the tree and accepts a prop called value (which can be anything).”
  • “The Consumer component is used anywhere below the provider in the tree and accepts a prop called “children” which must be a function that accepts the value and must return a react element (JSX).”

Building your own React-Router

The code of this example has a little more than 40 lines.

What we want?

We will want our application to show components when a given route matches the url.

Something like this:

<Route path="/"><DashboardContainer /></Route>
<Route path="/users"><UserContainer /></Route>
<Route path="/products"><ProductContainer /></Route>

And, of course, we want to be able to navigate to a certain url:

<Link path="/users">Users</Link>

Dependencies

I will not reinvent the wheel, we’ll use most the same dependencies as the React-Router itself.

To deal with pushstate we’ll use browser-history instead of history.

yarn add browser-history

To address the routes we will use pathToRegexp

yarn add path-to-regexp

Create a Router context container

First of all, we’ll need create a Context Container file where we will manage the router state and create the actions to navigate between urls.

In Router.js file we’ll add the following:

import React, { createContext } from 'react';
import history from 'browser-history';
const initialState = {
url: window.location.pathname
};
const Context = createContext()
const {Provider, Consumer} = Context;

The first 9 lines import necessary libs, initialize state, create a context object and extract Provider and Consumer from a Context.

We will use the Provider to keep the context and export the Consumer to be used by the App to have access to the state and actions.

class Router extends React.Component{
state = initialState;
action = {
go: (url) => this.setState(
state => ({...state, url}),
() => history(url)
)
};
componentDidMount() {
history((e, url) => this.setState(state=>({...state, url})));
}
render() {
return <Provider value={{state: this.state, action:this.action}}>{this.props.children}</Provider>;
}
}
export { Router as default, Consumer, };

Using Router Context Provider

In your app you could have something like this, and use the Router like this:

import Router from './Router';
//... import react, you toolbar and your content component
class App extends React.Component {
render() {
return (
<Router>
<Toobar />
<Content />
</Router>
);
}
}
export default App;

Now you can use Route and Link components, but first let’s implement this two first.

Route Component

Create a Route.js file and add this.

import React from 'react';
import pathToRegexp from 'path-to-regexp';
import { Consumer } from './Router';export default function Route(props) {
return (<Consumer>
{({state})=> {
const re = pathToRegexp(props.path);
if (re.test(state.url)) return props.children;
}}
</Consumer>);
}

Using your Route Component

For example, in your Content Component, you could have this code:

//...
import { Consumer } from './Router';
import Route from './Route';
export default function Content(props) {
return <Paper style={{padding:20, margin: 20}}>
<Consumer>
{({state, action}) => {
return <React.Fragment>
<Route path="/"><div>main</div></Route>
<Route path="/users"><UserContainer /></Route>
<Route path="/products"><ProductContainer /></Route>
</React.Fragment>
}}
</Consumer>
</Paper>;
}

As you see in the implementation of Route component ‘path’ will be tested to see if match with current state of Router Context Provider.

Link Component

To navigate between urls you can use the exposed actions by the Router Consumer directly:

import { Consumer } from './Router';
//...
<Consumer>
{({action}) => <React.Fragment>
<Button color="inherit" onClick={()=>action.go('/users')}>Users</Button>
<Button color="inherit" onClick={()=>action.go('/products')}>Products</Button>
</React.Fragment>}
</Consumer>

Or you can implement your own Link Component like this:

import React from 'react';
import { Consumer } from './Router';
export default function Link({path, ...props}) {
return (<Consumer>
{({action})=> <a {...props} onClick={()=>action.go(path)} />}
</Consumer>);
}

This kind implementations using context aren’t something new, they exist in a lot of famous libs, nonetheless I hope helped you to understand a little bit how you can use the New React Context API and, how easy it is to use in your own projects.

You can find the code on GitHub:

Thanks to Joaquim Ley (Joaquim Ley) for your review and your time.

Steven Koch

Written by

The Fork/TripAdvisor Web Engineer

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