preinit
preinit
lets you eagerly fetch and evaluate a stylesheet or external script.
preinit("https://example.com/script.js", {as: "script"});
Reference
preinit(href, options)
To preinit a script or stylesheet, call the preinit
function from react-dom
.
import { preinit } from 'react-dom';
function AppRoot() {
preinit("https://example.com/script.js", {as: "script"});
// ...
}
The preinit
function provides the browser with a hint that it should start downloading and executing the given resource, which can save time. Scripts that you preinit
are executed when they finish downloading. Stylesheets that you preinit are inserted into the document, which causes them to go into effect right away.
Parameters
href
: a string. The URL of the resource you want to download and execute.options
: an object. It contains the following properties:as
: a required string. The type of resource. Its possible values arescript
andstyle
.precedence
: a string. Required with stylesheets. Says where to insert the stylesheet relative to others. Stylesheets with higher precedence can override those with lower precedence. The possible values arereset
,low
,medium
,high
.crossOrigin
: a string. The CORS policy to use. Its possible values areanonymous
anduse-credentials
. It is required whenas
is set to"fetch"
.integrity
: a string. A cryptographic hash of the resource, to verify its authenticity.nonce
: a string. A cryptographic nonce to allow the resource when using a strict Content Security Policy.fetchPriority
: a string. Suggests a relative priority for fetching the resource. The possible values areauto
(the default),high
, andlow
.
Returns
preinit
returns nothing.
Caveats
- Multiple calls to
preinit
with the samehref
have the same effect as a single call. - In the browser, you can call
preinit
in any situation: while rendering a component, in an Effect, in an event handler, and so on. - In server-side rendering or when rendering Server Components,
preinit
only has an effect if you call it while rendering a component or in an async context originating from rendering a component. Any other calls will be ignored.
Usage
Preiniting when rendering
Call preinit
when rendering a component if you know that it or its children will use a specific resource, and you’re OK with the resource being evaluated and thereby taking effect immediately upon being downloaded.
Ejemplo 1 de 2: Preiniting an external script
import { preinit } from 'react-dom';
function AppRoot() {
preinit("https://example.com/script.js", {as: "script"});
return ...;
}
If you want the browser to download the script but not to execute it right away, use preload
instead. If you want to load an ESM module, use preinitModule
.
Preiniting in an event handler
Call preinit
in an event handler before transitioning to a page or state where external resources will be needed. This gets the process started earlier than if you call it during the rendering of the new page or state.
import { preinit } from 'react-dom';
function CallToAction() {
const onClick = () => {
preinit("https://example.com/wizardStyles.css", {as: "style"});
startWizard();
}
return (
<button onClick={onClick}>Start Wizard</button>
);
}