Need help. How to use a Custom Struct with EnumWindows?

My code:

const EnumParams = Struct({
	uiMsg:  W.UINT,
	wParam: W.WPARAM,
	lParam: W.LPARAM
});

var EP = new EnumParams;
	
EP.uiMsg = 0;
EP.wParam = 0;
EP.lParam = 42;

const WndEnumProc = ffi.Callback(
    W.BOOL, [W.HWND, ref.refType(EnumParams)],
    (hwnd, ep) => {
        // HERE I AM UNABLE TO USE ep members! How To?
        return 1;
    }
);

user32.EnumWindows( WndEnumProc, EP.ref() );

In the WndEnumProc callback, ep.uiMsg is undefined How to declare the callback, how to call EnumWindows passing a pointer to my custom struct, and finally how to use the menbers in the callback?

[somanuell]

No. I use a 32 bits node.exe, so that’s 4 and 32.

[somanuell]

First Working Version without an EnumParams allocation for each enumerated window:

const { DStruct: DS, DTypes: W, U } = require('win32-api');
const user32 = U.load(); 
const ffi = require('ffi-napi');
const ref = require('ref-napi');
const StructDi = require('ref-struct-di');
const Struct = StructDi(ref);

const EnumParams = Struct({
	uiMsg:  W.UINT,
	wParam: W.WPARAM,
	lParam: W.LPARAM
});

var EP = new EnumParams;
EP.uiMsg = 0;
EP.wApram = 0;
EP.lParam = 42;

const refType = EP.ref().ref().type;

const WndEnumProc = ffi.Callback(
	W.BOOL,	[W.HWND, W.LPARAM],
	(hwnd, ep) => {
		const buf = Buffer.alloc(4);
		buf.writeInt32LE(ep, 0);
		buf.type = refType;
		const EPObject = buf.deref().deref();
		console.log( 'EPObject.lParam is: ' + EPObject.lParam );
		console.log('First enumerated window is: ' + hwnd);
		return 0;
	}
);

user32.EnumWindows( WndEnumProc, EP.ref().address() );

node.exe testew.js gives:

EPObject.lParam is: 42
First enumerated window is: 196734

There is still a Buffer.alloc(4); at the beginning of the callback…