# How do I pass a Loadster variable into the browser so the page can read it?

> How to expose dataset variables and bot context to JavaScript running inside the page with Browser Bots.

Source: https://loadster.com/faqs/passing-loadster-variables-to-the-browser/

Loadster variables, like dataset values you grab with `bot.getVariable()`, live outside the browser, in your code
blocks. Sometimes you want one of those values available *inside* the browser, so an
[Evaluate Block](https://loadster.com/manual/browser-scripts/evaluate-blocks/) or the page's own JavaScript can pick it up.

The cleanest way to do this is `browser.setVariable(name, value)` in a [code block](https://loadster.com/manual/code-blocks/). It assigns
the value directly to the browser's `window` object, where it's available globally on the current page and persists
across navigations within the same bot.

## Using browser.setVariable

Here's a typical pattern: pull a value from a dataset, push it into the browser, then navigate to a page that uses it.

```javascript
// Grab a token from the dataset (or wherever else you have one)
const apiToken = bot.getVariable("apiToken");

// Push it onto window in the browser
browser.setVariable("apiToken", apiToken);

// If you navigate the variable persists across the navigation
browser.navigate("https://example.com/dashboard");

// Subsequent eval blocks (or scripts on the page) can read it
const echoed = browser.eval("window.apiToken");
```


You can pass any JSON-serializable value, including arrays and objects:

```javascript
browser.setVariable("testConfig", {
    userId: bot.getVariable("userId"),
    features: ["beta", "experimental"],
    iteration: bot.getIteration()
});
```


## Why not just use browser.eval?

You can absolutely build an `eval()` string yourself, but it gets messy. You may have to JSON-encode the value or
worry about escaping quote characters, and the resulting code is harder to read. `browser.setVariable()` skips all
that and hands the value over directly.

## What's supported

`browser.setVariable()` accepts the same kinds of values that JSON understands: strings, numbers, booleans, arrays,
plain objects, and `null`. Functions, DOM nodes, and class instances can't be passed through, since they don't survive
serialization.

The variable is set on `window` in the current page right away, and it's also re-applied on every navigation within the
same bot's browser session, so you don't have to set it again after each `browser.navigate()`. The variable is gone
once the bot's browser session ends, which usually means the end of the iteration (unless you've disabled
[clearing state between iterations](https://loadster.com/faqs/cookies-and-variables-between-iterations/)).