React Refetch
A simple, declarative, and composable way to fetch data for React components.
Installation
Requires React 0.14 or later.
npm install --save react-refetch
This assumes that youโre using npm package manager with a module bundler like Webpack or Browserify to consume CommonJS modules.
The following ES6 functions are required:
Check the compatibility tables (Object.assign
, Promise
, fetch
, Array.prototype.find
) to make sure all browsers and platforms you need to support have these, and include polyfills as necessary.
Introduction
See Introducing React Refetch on the Heroku Engineering Blog for background and a quick introduction to this project.
Motivation
This project was inspired by (and forked from) React Redux. Redux/Flux is a wonderful library/pattern for applications that need to maintain complicated client-side state; however, if your application is mostly fetching and rendering read-only data from a server, it can over-complicate the architecture to fetch data in actions, reduce it into the store, only to select it back out again. The other approach of fetching data inside the component and dumping it in local state is also messy and makes components smarter and more mutable than they need to be. This module allows you to wrap a component in a connect()
decorator like react-redux, but instead of mapping state to props, this lets you map props to URLs to props. This lets you keep your components completely stateless, describe data sources in a declarative manner, and delegate the complexities of data fetching to this module. Advanced options are also supported to lazy load data, poll for new data, and post data to the server.
Example
If you have a component called Profile
that has a userId
prop, you can wrap it in connect()
to map userId
to one or more requests and assign them to new props called userFetch
and likesFetch
:
import React, { Component } from 'react'
import { connect, PromiseState } from 'react-refetch'
class Profile extends Component {
render() {
// see below
}
}
export default connect(props => ({
userFetch: `/users/${props.userId}`,
likesFetch: `/users/${props.userId}/likes`
}))(Profile)
When the component mounts, the requests will be calculated, fetched, and the result will be passed into the component as the props specified. The result is represented as a PromiseState
, which is a synchronous representation of the fetch Promise
. It will either be pending
, fulfilled
, or rejected
. This makes it simple to reason about the fetch state at the point in time the component is rendered:
render() {
const { userFetch, likesFetch } = this.props
if (userFetch.pending) {
return <LoadingAnimation/>
} else if (userFetch.rejected) {
return <Error error={userFetch.reason}/>
} else if (userFetch.fulfilled) {
return <User user={userFetch.value}/>
}
// similar for `likesFetch`
}
See the composing responses to see how to handle userFetch
and likesFetch
together. Although not included in this library because of application-specific defaults, see an example PromiseStateContainer
and its example usage for a way to abstract and simplify the rendering of PromiseState
s.
Refetching
When new props are received, the requests are re-calculated, and if they changed, the data is refetched and passed into the component as new PromiseState
s. Using something like React Router to derive the props from the URL in the browser, the application can control state changes just by changing the URL. When the URL changes, the props change, which recalculates the requests, new data is fetched, and it is reinjected into the components:
By default, the requests are compared using their URL, headers, and body; however, if you want to use a custom value for the comparison, set the comparison
attribute on the request. This can be helpful when the request should or should not be refetched in response to a prop change that is not in the request itself. A common situation where this occurs is when two different requests should be refetched together even though one of the requests does not actually include the prop. Note, this is using the request object syntax for userStatsFetch
instead of just a plain URL string. This syntax allows for more advanced options. See the API documentation for details:
connect(props => ({
usersFetch: `/users?status=${props.status}&page=${props.page}`,
userStatsFetch: { url: `/users/stats`, comparison: `${props.status}:${props.page}` }
}))(UsersList)
In this example, usersFetch
is refetched every time props.status
or props.page
changes because the URL is changed. However, userStatsFetch
does not contain these props in its URL, so would not normally be refetched, but because we added comparison: ${props.status}:${props.page}
, it will be refetched along with usersFetch
. In general, you should only rely on changes to the requests themselves to control when data is refetched, but this technique can be helpful when finer-grained control is needed.
If you always want data to be refetched when any new props are received, set the force: true
option on the request. This will take precedence over any custom comparison
and the default request comparison. For example:
connect(props => ({
usersFetch: `/users?status=${props.status}&page=${props.page}`,
userStatsFetch: { url: `/users/stats`, force: true }
}))(UsersList)
Setting force: true
should be avoided if at all possible because it could result in extraneous data fetching and rendering of the component. Try to use the default comparison or custom comparison
option instead.
Automatic Refreshing
If the refreshInterval
option is provided along with a URL, the data will be refreshed that many milliseconds after the last successful response. If a request was ever rejected, it will not be refreshed or otherwise retried. In this example, likesFetch
will be refreshed every minute. Note, this is using the request object syntax for likeFetch
instead of just a plain URL string. This syntax allows for more advanced options. See the API documentation for details.
connect(props => ({
userFetch:`/users/${props.userId}`,
likesFetch: { url: `/users/${props.userId}/likes`, refreshInterval: 60000 }
}))(Profile)
When refreshing, the PromiseState
will be the same as the previous fulfilled
state, but with the refreshing
attribute set. That is, pending
will remain unset and the existing value
will be left intact. When the refresh completes, refreshing
will be unset and the value
will be updated with the latest data. If the refresh is rejected, the PromiseState
will move into a rejected
and not attempt to refresh again.
Fetch Functions
Instead of mapping the props directly to a URL string or request object, you can also map the props to a function that returns a URL string or request object. When the component receives props, instead of the data being fetched immediately and injected as a PromiseState
, the function is bound to the props and injected into the component as functional prop to be called later (usually in response to a user action). This can be used to either lazy load data, post data to the server, or refresh data. These are best shown with examples:
Lazy Loading
Here is a simple example of lazy loading the likesFetch
with a function:
connect(props => ({
userFetch: `/users/${props.userId}`,
lazyFetchLikes: max => ({
likesFetch: `/users/${props.userId}/likes?max=${max}`
})
}))(Profile)
In this example, userFetch
is fetched normally when the component receives props, but lazyFetchLikes
is a function that returns likesFetch
, so nothing is fetched immediately. Instead lazyFetchLikes
is injected into the component as a function to be called later inside the component:
this.props.lazyFetchLikes(10)
When this function is called, the request is calculated using both the bound props and any passed in arguments, and the likesFetch
result is injected into the component normally as a PromiseState
.
Posting Data
Functions can also be used for post data to the server in response to a user action. For example:
connect(props => ({
postLike: subject => ({
postLikeResponse: {
url: `/users/${props.userId}/likes`,
method: 'POST',
body: JSON.stringify({ subject })
}
})
}))(Profile)
The postLike
function is injected in as a prop, which can then be tied to a button:
<button onClick={() => this.props.postLike(someSubject)}>Like!</button>
When the user clicks the button, someSubject
is posted to the URL and the response is injected as a new postLikeResponse
prop as a PromiseState
to show progress and feedback to the user.
Manually Refreshing Data
Functions can also be used to manually refresh data by overwriting an existing PromiseState
:
connect(props => {
const url = `/users/${props.userId}`
return {
userFetch: url,
refreshUser: () => ({
userFetch: {
url,
force: true,
refreshing: true
}
})
}
})(Profile)
The userFetch
data is first loaded normally when the component receives props, but the refreshUser
function is also injected into the component. When this.props.refreshUser()
is called, the request is calculated, and compared with the existing userFetch
request. If the request changed (or force: true
), the data is refetched and the existing userFetch
PromiseState
is overwritten. This should generally only be used for user-invoked refreshes; see above for automatically refreshing on an interval.
Note, the example above sets force: true
and refreshing: true
on the request returned by the refreshUser()
function. These attributes are optional, but commonly used with manual refreshes. force: true
avoids the default request comparison (e.g. url
, method
, headers
, body
) with the existing userFetch
request so that every time this.props.refreshUser()
is called, a fetch is performed. Because the request would not have changed from the last prop change in the example above, force: true
is required in this case for the fetch to occur when this.props.refreshUser()
is called. refreshing: true
avoids the existing PromiseState
from being cleared while fetch is in progress.
Posting + Refreshing Data
The two examples above can be combined to post data to the server and refresh an existing PromiseState
. This is a common pattern when responding to a user action to update a resource and reflect that update in the component. For example, if PATCH /users/:user_id
responds with the updated user, it can be used to overwrite the existing userFetch
when the user updates her name:
connect(props => ({
userFetch: `/users/${props.userId}`,
updateUser: (firstName, lastName) => ({
userFetch: {
url: `/users/${props.userId}`
method: 'PATCH'
body: JSON.stringify({ firstName, lastName })
}
})
}))(Profile)
Composing Responses
If a component needs data from more than one URL, the PromiseState
s can be combined with PromiseState.all()
to be pending
until all the PromiseState
s have been fulfilled. For example:
render() {
const { userFetch, likesFetch } = this.props
// compose multiple PromiseStates together to wait on them as a whole
const allFetches = PromiseState.all([userFetch, likesFetch])
// render the different promise states
if (allFetches.pending) {
return <LoadingAnimation/>
} else if (allFetches.rejected) {
return <Error error={allFetches.reason}/>
} else if (allFetches.fulfilled) {
// decompose the PromiseState back into individual
const [user, likes] = allFetches.value
return (
<div>
<User data={user}/>
<Likes data={likes}/>
</div>
)
}
}
Similarly, PromiseState.race()
can be used to return the first settled PromiseState
. Like their asynchronous Promise
counterparts, PromiseStates
can be chained with then()
and catch()
; however, the handlers are run immediately to transform the existing state. This can be helpful to handle errors or transform values as part of a composition. For example, to provide a fallback value to likesFetch
in the case of failure:
PromiseState.all([userFetch, likesFetch.catch(reason => [])])
Chaining Requests
Inside of connect()
, requests can be chained using then()
, catch()
, andThen()
and andCatch()
to trigger additional requests after a previous request is fulfilled. These are not to be confused with the similar sounding functions on PromiseState
, which are on the response side, are synchronous, and are executed for every change of the PromiseState
.
then()
is helpful for cases where multiple requests are required to get the data needed by the component and the subsequent request relies on data from the previous request. For example, if you need to make a request to /foos/${name}
to look up foo.id
and then make a second request to /bar-for-foos-by-id/${foo.id}
and return the whole thing as barFetch
(the component will not have access to the intermediate foo
):
connect(({ name }) => ({
barFetch: {
url: `/foos/${name}`,
then: foo => `/bar-for-foos-by-id/${foo.id}`
}
}))
andThen()
is similar, but is intended for side effect requests where you still need access to the result of the first request and/or need to fanout to multiple requests:
connect(({ name }) => ({
fooFetch: {
url: `/foos/${name}`,
andThen: foo => ({
barFetch: `/bar-for-foos-by-id/${foo.id}`
})
}
}))
This is also helpful for cases where a fetch function is changing data that is in some other fetch that is a collection. For example, if you have a list of foo
s and you create a new foo
and the list needs to be refreshed:
connect(({ name }) => ({
foosFetch: '/foos',
createFoo: name => ({
fooCreation: {
method: 'POST',
url: '/foos',
andThen: () => ({
foosFetch: {
url: '/foos',
refreshing: true
}
})
}
})
}))
catch
and andCatch
are similar, but for error cases.
Identity Requests: Static Data & Transforming Responses
To support static data and response transformations, there is a special kind of request called an "identity request" that has a value
instead of a url
. The value
is passed through directly to the PromiseState
without actually fetching anything. In its pure form, it looks like this:
connect(props => ({
usersFetch: {
value: [
{
id: 1,
name: 'Jane Doe',
verified: true
},
{
id: 2,
name: 'John Doe',
verified: false
}
]
}
}))(Users)
In this case, the usersFetch
PromiseState
will be set to the provided list of users. The use case for identity requests by themselves is limited to mostly injecting static data during development and testing; however, they can be quite powerful when used with request chaining. For example, it is possible to fetch data from the server, filter it within a then
function, and return an identity request:
connect(props => ({
usersFetch: {
url: `/users`,
then: (users) => ({
value: users.filter(u => u.verified)
})
}
}))(Users)
Note, this form of transformation is similar to what is possible on the PromiseState
(i.e. this.props.usersFetch.then(users => users.filter(u => u.verified))
); however, this has the advantage of only being called when usersFetch
changes and keeps the logic out of the component.
Identity requests can also be provided a Promise
(or any "thenable") or a Function
.
If value
is a Promise
, the PromiseState
will be pending
until the Promise
is resolved. This can be helpful for asynchronous, non-fetch operations (e.g. file i/o) that want to use a similar pattern as fetch operations.
If value
is a Function
, it will be evaluated with no arguments and its return value will be used instead, as in cases described above. The Function
will only be called when comparison
changes. This can be helpful for cases where you want to provide an identify request, but it is expensive to evaluate. By wrapping it in a function, it is only evaluated when something changes.
connect(props => ({
userFetch: {
comparison: props.userId,
value: () => SomeExternalAPI.getUser(`/users/${props.userId}`)
}
}))(Users)
Accessing Headers & Metadata
Both request and response headers and other metadata are accessible. Custom request headers can be set on the request as an object:
connect(props => ({
userFetch: {
url: `/users/${props.userId}`,
headers: {
FOO: 'foo',
BAR: 'bar'
}
}
}))(Profile)
The raw Request
and Response
can be accessed via the meta
attribute on the PromiseState
. For example, to access the a response header:
userFetch.meta.response.headers.get('FOO')
Do not attempt to read bodies directly from meta.request
or meta.response
. They are provided for metadata purposes only.
Setting defaults and hooking into internal processing
It is possible to modify the various defaults used by React Refetch, as well as substitute in custom implementations of internal functions. A simple use case would be to avoid repeating the same option for every fetch block:
import { connect } from 'react-refetch'
const refetch = connect.defaults({
credentials: 'include'
})
refetch(props => ({
userFetch: `/users/${props.userId}`
}))(Profile)
A more advanced use case would be to replace the buildRequest
internal function to, for example, modify headers on the fly based on the URL of the request, or using advanced Request
options:
// api-connector.js
import { connect } from 'react-refetch'
import urlJoin from 'url-join'
import { getPrivateToken } from './api-tokens'
const baseUrl = 'https://api.example.com/'
export default connect.defaults({
buildRequest: function (mapping) {
const options = {
method: mapping.method,
cache: 'force-cache',
referrer: 'https://example.com',
headers: mapping.headers,
credentials: mapping.credentials,
redirect: mapping.redirect,
mode: mapping.mode,
body: mapping.body
}
if (mapping.url.match(/private/)) {
options.headers['X-Api-Token'] = getPrivateToken()
}
if (mapping.url.match(/listOfServers.json$/)) {
options.integrity = 'sha256-BpfBw7ivV8q2jLiT13fxDYAe2tJllusRSZ273h2nFSE='
}
return new Request(urlJoin(baseUrl, mapping.url), options)
}
})
// ProfileComponent.js
import connect from './api-connector'
connect(props => ({
userFetch: `/users/${props.userId}`,
serversFetch: `/listOfServers.json`
}))(Profile)
You can also replace the handleResponse
function, which takes a Response
, and should return a Promise that resolves to the value of the response, or rejects based on the body, headers, status code, etc. You can use it, for example, to parse CSV instead of JSON:
// api-connector.js
import { connect } from 'react-refetch'
import { parse } from 'csv'
const csvConnector = connect.defaults({
handleResponse: function (response) {
if (response.headers.get('content-length') === '0' || response.status === 204) {
return
}
const csv = response.text()
if (response.status >= 200 && response.status < 300) {
return csv.then(text => new Promise((resolve, reject) => {
parse(text, (err, data) => {
if (err) { reject(err) }
resolve(data)
})
}))
} else {
return csv.then(cause => Promise.reject(new Error(cause)))
}
}
})
csvConnector(props => ({
userFetch: `/users/${props.userId}.csv`
}))(Profile)
fetch
and Request
implementations
On changing the Through this same API it is possible to change the internal fetch
and Request
implementations. This could be useful for a number of reasons, such as precise control over requests or customisation that is not possible with either buildRequest
or handleResponse
.
For example, here's a simplistic implementation of a "caching fetch," which will cache the result of successful requests for a minute, regardless of headers:
import { connect } from 'react-refetch'
const cache = new Map()
function cachingFetch(input, init) {
const req = new Request(input, init)
const now = new Date().getTime()
const oneMinuteAgo = now - 60000
const cached = cache.get(req.url)
if (cached && cached.time < oneMinuteAgo) {
return new Promise(resolve => resolve(cached.response.clone()))
}
return fetch(req).then(response => {
cache.set(req.url, {
time: now,
response: response.clone()
})
return response
})
}
connect.defaults({ fetch: cachingFetch })(props => ({
userFetch: `/users/${props.userId}`
}))(Profile)
When using this feature, make sure to read the fetch
API and interface documentation and all related topics. Notably, you need to keep in mind that the body
of a Response
can only be consumed once, so if you need to read it in your custom fetch
, you also need to recreate a brand new Response
(or a .clone()
of the original one if you're not modifying the body) so React Refetch can work properly.
This is an advanced feature. Use existing declarative functionality wherever possible. Customise buildRequest
or handleResponse
if these can work instead. Please be aware that changing the fetch
(or Request
) implementation could conflict with built-in current or future functionality.
Unit Testing Connected Components
For unit testing components connected, a non-default export of the unconnected component can be exposed to allow unit tests to inject their own PromiseState
(s) as props. This allows for unit tests to test both success and error scenarios without having to deal with mocking HTTP, timing of responses, or other details about how the PromiseState
(s) is fulfilled -- instead, they can just focus on asserting that the component itself renders the PromiseState
(s) correctly in various scenarios.
The recommended naming convention for the unconnected component is to prepend an underscore to the component name. For example, if there is a component called Profile
, add a non-default export of _Profile
before the default export with connect
:
class Profile extends React.Component {
static propTypes = {
userFetch: PropTypes.instanceOf(PromiseState).isRequired,
}
render() {
const { userFetch } = this.props
if (userFetch.pending) {
return <LoadingAnimation/>
} else if (userFetch.rejected) {
return <ErrorBox error={userFetch.reason}/>
} else if (userFetch.fulfilled) {
return <User user={userFetch.value}/>
}
}
}
export { Profile as _Profile }
export default connect(props => ({
userFetch: `/users/${props.userId}`
}))(Profile)
Now, unit tests can use the static methods on PromiseState
to inject their own PromiseState
(s) as props. For example, here is a unit test using Enzyme to shallow render the unconnected _Profile
and provides a pending PromiseState
and asserts that the LoadingAnimation
is present:
const c = shallow(
<_Profile
userFetch={PromiseState.create()}
/>
)
expect(wrapper.find(LoadingAnimation)).to.have.length(1)
Similarly, the rejected and fulfilled cases can be tested:
const expectedError = new Error('boom')
const c = shallow(
<_Profile
userFetch={PromiseState.reject(expectedError)}
/>
)
expect(c.find(ErrorBox).first().prop().error).toEqual(expectedError)
const user = new User()
const c = shallow(
<_Profile
userFetch={PromiseState.resolve(user)}
/>
)
expect(wrapper.find(User)).to.have.length(1)
Complete Example
This is a complex example demonstrating various feature at once:
import React, { Component, PropTypes } from 'react'
import { connect, PromiseState } from 'react-refetch'
class Profile extends React.Component {
static propTypes = {
params: PropTypes.shape({
userId: PropTypes.string.isRequired,
}).isRequired,
userFetch: PropTypes.instanceOf(PromiseState).isRequired
likesFetch: PropTypes.instanceOf(PromiseState).isRequired
updateStatus: PropTypes.func.isRequired
updateStatusResponse: PropTypes.instanceOf(PromiseState) // will not be set until after `updateStatus()` is called
}
render() {
const { userFetch, likesFetch } = this.props
// compose multiple PromiseStates together to wait on them as a whole
const allFetches = PromiseState.all([userFetch, likesFetch])
// render the different promise states
if (allFetches.pending) {
return <LoadingAnimation/>
} else if (allFetches.rejected) {
return <Error error={allFetches.reason}/>
} else if (allFetches.fulfilled) {
// decompose the PromiseState back into individual
const [user, likes] = allFetches.value
return (
<div>
<User data={user}/>
<Likes data={likes}/>
</div>
)
}
// call `updateStatus()` on button click
<button onClick={() => { this.props.updateStatus("Hello World")} }>Update Status</button>
if (updateStatusResponse) {
// render the different promise states, but will be `null` until `updateStatus()` is called
}
}
}
// declare the requests for fetching the data, assign them props, and connect to the component.
export default connect(props => {
return {
// simple GET from a URL injected as `userFetch` prop
// if `userId` changes, data will be refetched
userFetch: `/users/${props.params.userId}`,
// similar to `userFetch`, but using object syntax
// specifies a refresh interval to poll for new data
likesFetch: {
url: `/users/${props.userId}/likes`,
refreshInterval: 60000
},
// declaring a request as a function
// not immediately fetched, but rather bound to the `userId` prop and injected as `updateStatus` prop
// when `updateStatus` is called, the `status` is posted and the response is injected as `updateStatusResponse` prop.
updateStatus: status => ({
updateStatusResponse: {
url: `/users/${props.params.userId}/status`,
method: 'POST',
body: status
}
})
}
})(Profile)
TypeScript
If you are using React Refetch in a project that is using TypeScript, this library ships with type definitions.
Below is an example connected component in TypeScript. Note how there is both an OuterProps
and InnerProps
. The OuterProp
are the props the component receives from the outside. In this example, the OuterProps
would just be userId: string
the caller is expected to pass in (e.g. <UserWidget userId="user-123"/>
). The InnerProps
are the PromiseState
props that the connect()
function injects into the component when fetching data. Since the InnerProps
include the OuterProps
, they are defined as InnerProps extends OuterProps
and then the component itself extends React.Component<InnerProps>
. This allows the component to have access to both the userId: string
and userFetch: PromiseState<User>
internally. However, the connect
function returns a component with only the OuterProps
(e.g. React.Component<OuterProps>
) so callers only need to pass in userId: string
.
interface OuterProps {
userId: string
}
interface InnerProps extends OuterProps {
userFetch: PromiseState<User>
}
class UserWidget extends React.Component<InnerProps> {
render() {
return (
<ul>
<li>{ this.props.userId }</li>
<li>{ this.props.userFetch.fulfilled && this.props.userFetch.value.name }</li>
</ul>
)
}
}
export default connect<OuterProps, InnerProps>((props) => ({
userFetch: `/users/${props.userId}`
}))(UserWidget)
API Documentation
Support
This software is provided "as is", without warranty or support of any kind, express or implied. See license for details.