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injectFilter()

The injectFilter() hook allows you to control where and what tags Vike injects in the HTML, most notably preload tags.

If you merely want to change the position of scripts, you can use the injectScriptsAt setting instead.

Vite also injects preload tags, see Vite > Config > build.modulePreload.

Examples

Usage

injectFilter() is called only in production: it has no effect in development. (Because, in development, the dependency graph is lazily discovered and therefore not fully known upon rendering HTML.)

⚠️
injectFilter() is a beta feature. (Which means breaking changes may occur during any minor version update.)
// /renderer/+onRenderHtml.ts
 
export { onRenderHtml }
 
import type { InjectFilterEntry } from 'vike/types'
 
async function onRenderHtml(pageContext) {
  // ...
 
  const documentHtml = escapeInject`<!DOCTYPE html>
    <html>
      <body>
        <div id="page-view">${stream}</div>
      </body>
    </html>`
 
  const injectFilter = (assets: InjectFilterEntry[]): void => {
    assets.forEach(asset => {
      if (
        // We don't touch entry assets (recommended)
        asset.isEntry ||
        // We don't touch JavaScript preloading (recommended)
        asset.assetType === 'script'
      ) {
        return
      }
 
      // Preload images
      if (asset.assetType === 'image') {
        asset.inject = 'HTML_BEGIN'
      }
 
      // Don't preload fonts
      if (asset.assetType === 'font') {
        asset.inject = false
      }
 
      // Preload videos
      if (asset.mediaType?.startsWith('video')) {
        asset.inject = 'HTML_END'
      }
    })
  }
 
  return { documentHtml, injectFilter }
}
type InjectFilterEntry = {
  inject: false | 'HTML_BEGIN' | 'HTML_END' // Whether and where to inject
  src: string // Asset's URL
  assetType: "image" | "script" | "font" | "style" | "audio" | "video" | "document" |
             "fetch" | "track" | "worker" | "embed" | "object" | null
  mediaType: string // MIME type
  isEntry: boolean // true  ⇒ <script> or <link rel="stylesheet" type="text/css">
                   // false ⇒ preload tag, e.g. <link rel="preload" as="font">
}

See also