React Tunnels ? 
Render React components in placeholders that are placed somewhere else in the component tree.
Install
yarn add react-tunnels
Why
There is a common use case in React apps where you want to define a Layout where the content of some elements is defined by children components. For example, you want to define Layout just once and reuse it for every page but it has a breadcrumb whose steps depend on children components. This tiny library allows you to define tunnels to render from an element to whatever another element in the App, even elements located on top of the tree. It's like Portal but the target is a component instead of a DOM element.
Usage
Define a TunnelPlaceholder identified by an id and decide what properties are going to be passed to its render function by defining Tunnel components with the same id anywhere else in the app. If you define just a single Tunnel its props will be passed straight to the render function, if there is more than one Tunnel for a single id, the placeholder render function will receive an item argument which is an Array containing the props for each Tunnel. Let's see some examples.
Simple example: children tunneling
Define a placeholder without any render function so it will render any children coming from a Tunnel component with the same id.
import { TunnelProvider, TunnelPlaceholder, Tunnel } from 'react-tunnels'
render(
<TunnelProvider>
<div>
<TunnelPlaceholder id="my-tunnel" />
<Tunnel id="my-tunnel">
This will be rendered on the placeholder ?
</Tunnel>
</div>
</TunnelProvider>
)
Check the real example here
More complex example: building a Breadcrumb
It's easy to build a breadcrumb using the prop multiple in the TunnelPlaceholder. This allows to let it know that there will be multiple tunnels so the render function will be called with an array of props.
const Breadcrumbs = () => (
<TunnelPlaceholder id="breadcrumb" multiple>
{({ items }) => (
items.map(({ children, href }) => (
<span><a href={href}>{children}</a></span>
))
)}
</TunnelPlaceholder>
)
const Breadcrumb = ({ children, url }) => (
<Tunnel id="breadcrumb" href={url}>
{children}
</Tunnel>
)
render(
<TunnelProvider>
{/* This will render the breadcrumb */}
<Breadcrumbs />
{/* Somewhere else in children */}
<Breadcrumb url="/products">Products</Breadcrumb>
<Breadcrumb url="/products/123">Product <strong>123</strong></Breadcrumb>
</TunnelProvider>
)
Check the live example here
Similar Libraries
- React Slot Fill: A similar project built by Cameron Westland with a slightly different API and a bit more limited use cases. The main difference is that you can't pass content to a placeholder from multiple entry points. react-tunnels does this by passing an array with the props defined by each tunnel to the render function of the placeholder. For simple cases though, it is pretty similar.
- Preact Slots: A library similar to React Slot Fill but for Preact developed by Jason Miller.
About
This project has been developed by Javi Velasco as a way to build Breadcrumb components and Layout customizations for a variety of React projects. Any feeback, help or improvements is highly appreciated.
License
This project is licensed under the terms of the MIT license.