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Caching actions in Stagehand is useful for actions that are expensive to run, or when the underlying DOM structure is not expected to change.

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Using observe to preview an action

observe lets you preview an action before taking it. If you are satisfied with the action preview, you can run it in page.act with no further LLM calls. 
const [actionPreview] = await page.observe("Click the quickstart link");

/** actionPreview is a JSON-ified version of a Playwright action:
{
	description: "The quickstart link",
	method: "click",
	selector: "/html/body/div[1]/div[1]/a",
	arguments: [],
}
**/

// NO LLM INFERENCE when calling act on the preview
await page.act(actionPreview)

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Simple caching

Let’s use a simple file-based cache for this example. We’ll write a getter and a setter functions that can read and write to a JSON file: 
// Get the cached value (undefined if it doesn't exist)
async function getCache(key: string): Promise<ObserveResult | undefined> {
  try {
    const cache = await readFile("cache.json");
    const parsed = JSON.parse(cache);
    return parsed[key];
  } catch {
    return undefined;
  }
}

// Set the cache value
async function setCache(key: string, value: ObserveResult): Promise<void> {
  const cache = await readFile("cache.json");
  const parsed = JSON.parse(cache);
  parsed[key] = value;
  await writeFile("cache.json", JSON.stringify(parsed));
}

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Act with cache

Let’s write a function that will check the cache, get the action, and run it. If the action fails, we’ll attempt to “self-heal”, i.e. retry it with page.act directly. 
// Check the cache, get the action, and run it
// If selfHeal is true, we'll attempt to self-heal if the action fails
async function actWithCache(page: Page, key: string, prompt: string, selfHeal = false) {
	try {
		const cacheExists = await getCache(key);

		let action: ObserveResult;
		if (cacheExists) {
		// Get the cached action
		action = await getCache(prompt);
		} else {
		// Get the observe result (the action)
		[action] = await page.observe(prompt);

		// Cache the action
		await setCache(prompt, action);
		}

		// Run the action (no LLM inference)
		await page.act(action);
	} catch (e) {
		console.error(e);
		// in selfHeal mode, we'll retry the action
		if (selfHeal) {
			console.log("Attempting to self-heal...");
			await page.act(prompt);
		}
		else {
			throw e;
		}
	}
}
You can now use actWithCache to run an action with caching: 
const prompt = "Click the quickstart link";
const key = prompt; // Simple cache key
// Attempt cached action or self-heal
await actWithCache(page, key, prompt);

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Advanced caching

The above example is simple, but you may want to cache actions based on the page contents. Also, if you have duplicate prompts, you should use a more unique key. We want to leave caching logic up to you, but give you all the tools you need to implement your own caching strategy. You can directly access the DOM and accessibility tree from Playwright’s page object. Here’s an example of how to access the page content: 
// Get the page content
const pageContent = await page.content();
You may also want to use the accessibility tree, the DOM, or any other information to create a more unique key. You can do this as you please, with very similar logic to the above example.
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