Cache Hooks

Cache Hooks

There are cases where you want to modify the html that is served from cache or the html that is generated on the fly.

For example, you might want to add some tracking scripts to the html that is served from cache. Or you might want to add some custom html to the html that is generated on the fly.

To do that, you can use the modifyCachedHtml and modifyGeneratedHtml callbacks.

modifyCachedHtml

The modifyCachedHtml callback is called when the html is served from cache (on every user request). It receives the request and the cached html as parameters. It should return the modified html.

modifyGeneratedHtml

The modifyGeneratedHtml callback is called when the html is generated on the fly (before the cache is stored). It receives the request and the generated html as parameters. It should return the modified html.

Example

server.get(
  '*',
  // Serve page if it exists in cache
  async (req, res, next) =>
    await isr.serveFromCache(req, res, next, {
      modifyCachedHtml: (req, cachedHtml) => {
        return `${cachedHtml}<!-- Hello, I'm a modification to the original cache! -->`;
      },
    }),
  // Server side render the page and add to cache if needed
  async (req, res, next) =>
    await isr.render(req, res, next, {
      modifyGeneratedHtml: (req, html) => {
        return `${html}<!-- Hello, I'm modifying the generatedHtml before caching it! -->`;
      },
    })
);

Important:

Use these methods with caution as the logic written can increase the processing time.