# JSStringGetUTF8CString(_:_:_:) Converts a JavaScript string into a null-terminated UTF-8 string, and copies the result into an external byte buffer. ``` func JSStringGetUTF8CString(_ string: JSStringRef!, _ buffer: UnsafeMutablePointer!, _ bufferSize: Int) -> Int ``` ## Parameters `string` The source [`JSStringRef`](/documentation/JavaScriptCore/JSStringRef). `buffer` The destination byte buffer to copy a null-terminated UTF-8 representation of `string` into. On return, `buffer` contains a UTF-8 string representation of `string`. If `bufferSize` is too small, `buffer` contains only partial results. If `buffer` isn’t at least `bufferSize` bytes in size, the conversion results in undefined behavior. `bufferSize` The size of the external buffer in bytes. ## Return Value The number of bytes the system writes into `buffer` (including the null-terminator byte). ## Discussion --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)