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Some C APIs expect function pointers as arguments. arkffi provides CFunction to wrap them.

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Obtaining a Pointer

const handle = ffi.load('libffi_target.so');
const ptr = ffi.getSymbolPtr(handle, 'add');
// ptr is the memory address of the C function

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Creating a CFunction Wrapper

import { CFunction, FFIType } from 'arkffi';

const add = CFunction({
  args: [FFIType.double, FFIType.double],
  returns: FFIType.double,
  ptr: ptr,
});

add(2.0, 3.0); // → 5.0
add.close();

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Lifecycle

Always close wrappers when done: 
const fn = CFunction({ ... });
fn();
fn.close();

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Passing to C APIs

// C: void sort(int* arr, int (*cmp)(int, int));
const cmp = CFunction({ args: ['i', 'i'], returns: 'i', ptr: cmpPtr });
ffi.callMixed(handle, 'sort', 'ip', 'v', [arrPtr, cmp.ptr], []);

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Using JSCallback Instead

For TypeScript-to-C callbacks, use JSCallback: 
const cmp = new JSCallback(
  (a: number, b: number): number => a - b,
  { args: [FFIType.int32, FFIType.int32], returns: FFIType.int32 },
);

ffi.callMixed(handle, 'sort', 'ip', 'v', [arrPtr, cmp.ptr], []);
cmp.close();