> Portal Navigation:
> 
> - Append `.md` to any URL under `https://dev.wix.com/docs/` to get its markdown version.
> - Pages are either content pages (article or reference text) or menu pages (a list of links to child pages).
> - To get a menu page, truncate any URL to a parent path and append `.md` (e.g. `https://dev.wix.com/docs/sdk.md`, `https://dev.wix.com/docs/sdk/core-modules.md`).
> - Top-level index of all portals: https://dev.wix.com/docs/llms.txt
> - Full concatenated docs: https://dev.wix.com/docs/llms-full.txt

# Method name:

siteWindow.set(key: string, data: any)

# Method Link:

https://dev.wix.com/docs/sdk/frontend-modules/window/warmup-data/set.md

# Method Description:

Sets data in server-side code for use in client-side code.

A performance best practice is to set warmup data for time-consuming operations, such as querying
 collections or working with the results of network requests from external sites. You can write code that
 sets the data from these operations as warmup data on the server. The client-side code can then `get` that data without
 performing the operations again.

 You can only set warmup data on the server. This method has no effect if called from client-side code.

 > **Notes:**
 > + Rendering never occurs server-side when previewing a site.
 > + Server-side rendering only occurs when site visitors initially enter a site, and not when site visitors navigate from page-to-page in a site.

# Method Permissions:



# Method Permissions Scopes IDs:

undefined



# Method Code Examples:

## Set the warmup data on the server

```javascript
import { warmupData, rendering } from '@wix/site-window';

//...

if (await rendering.env() === "backend") {
  await warmupData.set("myWarmupMessage", "Now rendering on the server.");
}
```

## Use warmup data to send already-retrieved query results from the server to the client-side

```javascript
import { items } from "@wix/data";
import { warmupData, rendering } from '@wix/site-window';

async function getData() {
  const results = await items.query("MyCollection")
    .find();
  if (await rendering.env() === "backend") {
    await warmupData.set("myWarmupData", results.items);
    await warmupData.set("myWarmupMessage", "Rendering on the server.");
  }
  return results;
}

$w.onReady(async function () {
  const defaultMessage = "Rendering client-side."
  const dataResults = await warmupData.get("myWarmupData") || await getData();
  const message = await warmupData.get("myWarmupMessage") || defaultMessage;
  $w("#retrievedData").text = JSON.stringify(dataResults);
  $w("#retrievedMessage").text = message;
});
```