ffi.JSCallback.constructor

interface FFIFunction

• readonly args?: readonly FFITypeOrString[]

  Arguments to an FFI function (C ABI)

  Defaults to an empty array, which means no arguments.

  To pass a pointer, use "ptr" or "pointer" as the type name. To get a pointer, see ptr.

  From JavaScript:

  import { dlopen, FFIType, suffix } from "bun:ffi"
  
  const lib = dlopen(`adder.${suffix}`, {
  	add: {
  		// FFIType can be used or you can pass string labels.
  		args: [FFIType.i32, "i32"],
  		returns: "i32",
  	},
  })
  lib.symbols.add(1, 2)

  In C:

  int add(int a, int b) {
    return a + b;
  }

• readonly ptr?: bigint | Pointer

  Function pointer to the native function

  If provided, Bun uses this pointer instead of looking the function up with dlsym(). It should not be null (0).

  Use this when the library is already loaded, or when the module is also using Node-API.

• readonly returns?: FFITypeOrString

  Return type of an FFI function (C ABI)

  Defaults to FFIType.void

  To pass a pointer, use "ptr" or "pointer" as the type name. To get a pointer, see ptr.

  From JavaScript:

  import { dlopen, CString } from "bun:ffi"
  
  const lib = dlopen('z', {
     version: {
       returns: "ptr",
    }
  });
  console.log(new CString(lib.symbols.version()));

  In C:

  char* version()
  {
   return "1.0.0";
  }

• readonly threadsafe?: boolean

  Whether C/FFI code can call this function from a separate thread.

  Only supported with JSCallback.

  This does not make the function run in a separate thread; the application or library is still responsible for its own threading.

  Enabling it adds a small cost to every call, so it's only worth it when that cost is smaller than what you gain from running the function on a separate thread.

• readonly ptr: null | Pointer

  The pointer to the C function

  Becomes null once JSCallback.prototype.close is called

• readonly threadsafe: boolean

  Whether the callback can be called from a different thread

• close(): void;

  Free the memory allocated for the callback

  If called multiple times, does nothing after the first call.