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Introduction

PreSWR is a wrapper over swr that keeps track of your calls and lets you preload its results. It's oriented as a tool to help with Server-Side Rendering, and quite suited for use with Next.js, although its design is environment-agnostic.

$ yarn add preswr
import usePreSWR, { preloaded } from "preswr"
import React from "react"

const FavouritePokemon = preloaded(({ name }) => {
  const { data } = usePreSWR(`https://pokeapi.co/api/v2/pokemon/${name}/`)
  return (
    <p>
      My favourite Pokémon is ${data.name}, of type ${data.types[0].type.name}
    </p>
  )
})

export default FavouritePokemon.Component

export const getStaticProps = async ({ params }) =>
  await FavouritePokemon.preloadData({ name: params.name })

Usage

usePreSWR

The default export is the hook function usePreSWR, which wraps useSWR with the preloading smarts. It has the same arguments.

It is allowed to mix usePreSWR calls and useSWR calls freely, but only the usePreSWR will be preloaded.

PreSWRConfig

usePreSWR can't read the config from the <SWRConfig> provider. We export a <PreSWRConfig> that works for both.

preloaded

It's a function which takes a React component, and an optional options object, and returns an object with two properties.

preloaded(
  MyComponent,
  /* this object, and all its properties, are optional */
  {
    /**
     * PreSWR analyzes the tree multiple times to make sure that all
     * conditional rendering is taken care of. You can configure how many times
     * this can happen, or set `false` to disable deep analyzing.
     */
    maxDepth: 20,
  }
)
  • Component is your original component, but it takes an extra prop with the preloaded data. You need to use this component in place of the original one to take advantage of the preloading.

  • preloadData() takes the props you'd call your component with, preloads the data which it would request, and returns the props with an extra one which holds the preloaded data.

Limitations

  • It only works with ReactDOM, so no support for React Native (yet?)
  • Make sure you follow the Rules of Hooks
  • When preloadData is called, your React component is rendered in the background (maybe multiple times!), which might invoke side-effects if your code uses them.
  • Your fetcher functions must work in the context you're using preloadData(). You can provide an initialData config key in the call to bypass calling them.
  • Your keys (or the value returned from key functions) must be able to be serialized to JSON (that means numbers, strings, null, arrays, and plain objects).

TypeScript

This package is written in TypeScript, and it exports a number of helpful types.

An especially useful type is PreloaderProps<...>, which returns the type of the props of the wrapped component, including the extra internal prop which holds the preloaded data.

import { GetStaticProps } from "next"
import { preloaded, PreloaderProps } from "preswr"
import FooComponent from "./foo"

const PreloadedFoo = preloaded(FooComponent)

export default PreloadedFoo.Component

export const getStaticProps: GetStaticProps<PreloaderProps<
  typeof PreloadedFoo
>> = async ({ params }) =>
  await FavouritePokemon.preloadData({ name: params.name })

About

Preload your SWR hooks on the server

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