> ## Documentation Index
> Fetch the complete documentation index at: https://docs.smooth.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# Evaluate JS

> Execute JavaScript in the browser context

Execute JavaScript code in the browser context. This is useful for advanced interactions, reading page state, or performing actions that require direct DOM manipulation.

## Usage

<CodeGroup>
  ```python Python theme={null}
  from smooth import SmoothClient

  client = SmoothClient()

  with client.session() as session:
      session.goto("https://example.com")

      # Get the page title
      result = session.evaluate_js("document.title")
      print(f"Page title: {result.output}")
  ```
</CodeGroup>

## Request

<ResponseField name="code" type="string" required>
  The JavaScript code to execute in the browser. The code should be an expression or a function that returns a value.

  Example: `document.title`
</ResponseField>

<ResponseField name="args" type="dict">
  Optional dictionary of arguments to pass to the JavaScript function. When using args, your code must be a function that receives `args` as its parameter.

  Example: `{"selector": ".product-price", "index": 0}`
</ResponseField>

## Response

Returns an object with the following attributes.

<ResponseField name="output" type="any">
  The result of the JavaScript evaluation. Complex objects are serialized to JSON.
</ResponseField>

<ResponseField name="credits_used" type="float">
  The number of credits used for this action. 1 credit corresponds to \$0.01.
</ResponseField>

<ResponseField name="duration" type="float">
  The duration in seconds taken to execute the JavaScript.
</ResponseField>

## Examples

**Read page information:**

<CodeGroup>
  ```python Python theme={null}
  with client.session() as session:
      session.goto("https://example.com")

      # Get current URL
      result = session.evaluate_js("window.location.href")
      print(f"Current URL: {result.output}")

      # Get page title
      result = session.evaluate_js("document.title")
      print(f"Title: {result.output}")

      # Check if an element exists
      result = session.evaluate_js("!!document.querySelector('.login-button')")
      print(f"Has login button: {result.output}")
  ```
</CodeGroup>

**Extract data from the DOM:**

<CodeGroup>
  ```python Python theme={null}
  with client.session() as session:
      session.goto("https://example.com/products")

      result = session.evaluate_js("""
          Array.from(document.querySelectorAll('.product-card')).map(card => ({
              name: card.querySelector('.name').textContent,
              price: parseFloat(card.querySelector('.price').textContent.replace('$', ''))
          }))
      """)

      for product in result.output:
          print(f"{product['name']}: ${product['price']}")
  ```
</CodeGroup>

**With arguments:**

<CodeGroup>
  ```python Python theme={null}
  with client.session() as session:
      session.goto("https://example.com")

      result = session.evaluate_js(
          "(args) => { return document.querySelectorAll(args.selector).length; }",
          args={"selector": ".product-item"}
      )
      print(f"Found {result.output} products")
  ```
</CodeGroup>

**Scroll the page:**

<CodeGroup>
  ```python Python theme={null}
  with client.session() as session:
      session.goto("https://example.com/infinite-scroll")

      # Scroll to bottom to load more content
      session.evaluate_js("window.scrollTo(0, document.body.scrollHeight)")

      # Wait a moment for content to load, then extract
      session.run_task("Wait for new content to load")
      data = session.extract({"type": "array", "items": {"type": "object", "properties": {"title": {"type": "string"}}}})
  ```
</CodeGroup>

**Interact with page elements:**

<CodeGroup>
  ```python Python theme={null}
  with client.session() as session:
      session.goto("https://example.com/form")

      # Set a value directly
      session.evaluate_js(
          "(args) => { document.querySelector(args.selector).value = args.value; }",
          args={"selector": "#email", "value": "test@example.com"}
      )

      # Click a button
      session.evaluate_js("document.querySelector('#submit-btn').click()")
  ```
</CodeGroup>

**Check page state before proceeding:**

<CodeGroup>
  ```python Python theme={null}
  with client.session() as session:
      session.goto("https://example.com")
      session.run_task("Log in with my credentials")

      # Verify login succeeded
      result = session.evaluate_js("""
          {
              isLoggedIn: !!document.querySelector('.user-avatar'),
              username: document.querySelector('.username')?.textContent || null
          }
      """)

      if result.output['isLoggedIn']:
          print(f"Logged in as {result.output['username']}")
          session.run_task("Go to my account settings")
      else:
          print("Login failed")
  ```
</CodeGroup>