preinitModule

preinitModule("https://example.com/module.js", {as: "script"});

• Reference
  • preinitModule(href, options)
• Usage
  • Preloading when rendering
  • Preloading in an event handler

Reference

preinitModule(href, options)

To preinit an ESM module, call the preinitModule function from react-dom.

import { preinitModule } from 'react-dom';

function AppRoot() {
  preinitModule("https://example.com/module.js", {as: "script"});
  // ...
}

See more examples below.

The preinitModule function provides the browser with a hint that it should start downloading and executing the given module, which can save time. Modules that you preinit are executed when they finish downloading.

Parameters

• href: a string. The URL of the module you want to download and execute.
• options: an object. It contains the following properties:
  • as: a required string. It must be 'script'.
  • crossOrigin: a string. The CORS policy to use. Its possible values are anonymous and use-credentials.
  • integrity: a string. A cryptographic hash of the module, to verify its authenticity.
  • nonce: a string. A cryptographic nonce to allow the module when using a strict Content Security Policy.

Returns

preinitModule returns nothing.

Caveats

• Multiple calls to preinitModule with the same href have the same effect as a single call.
• In the browser, you can call preinitModule 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, preinitModule 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

Preloading when rendering

Call preinitModule when rendering a component if you know that it or its children will use a specific module and you’re OK with the module being evaluated and thereby taking effect immediately upon being downloaded.

import { preinitModule } from 'react-dom';

function AppRoot() {
  preinitModule("https://example.com/module.js", {as: "script"});
  return ...;
}

If you want the browser to download the module but not to execute it right away, use preloadModule instead. If you want to preinit a script that isn’t an ESM module, use preinit.

Preloading in an event handler

Call preinitModule in an event handler before transitioning to a page or state where the module will be needed. This gets the process started earlier than if you call it during the rendering of the new page or state.

import { preinitModule } from 'react-dom';

function CallToAction() {
  const onClick = () => {
    preinitModule("https://example.com/module.js", {as: "script"});
    startWizard();
  }
  return (
    <button onClick={onClick}>Start Wizard</button>
  );
}