---
title: "stringByEvaluatingJavaScript(from:)"
framework: uikit
role: symbol
role_heading: Instance Method
path: "uikit/uiwebview/stringbyevaluatingjavascript(from:)"
---

# stringByEvaluatingJavaScript(from:)

Returns the result of running a JavaScript script.

## Declaration

```swift
func stringByEvaluatingJavaScript(from script: String) -> String?
```

## Parameters

- `script`: The JavaScript script to run.

## Return Value

Return Value The result of running the JavaScript script passed in the script parameter, or nil if the script fails.

## Discussion

Discussion New apps should instead use the evaluateJavaScript(_:completionHandler:) method from the WKWebView class. Legacy apps should adopt that method if possible. important: The stringByEvaluatingJavaScript(from:) method waits synchronously for JavaScript evaluation to complete. If you load web content whose JavaScript code you have not vetted, invoking this method could hang your app. Best practice is to adopt the WKWebView class and use its evaluateJavaScript(_:completionHandler:) method instead.