getLastError

Calls the windows GetLastError function when failed calling other functions with ffi-napi library.

Unfortunately, you cannot use the async mode of the specific function if you want to get the error code, because the ffi-napi library will also call some apis that will clear the error.

To successfully get the error code, please use the sync mode of the specific function.

This project was born as an experiment to learn C++, so consider that there might be bugs, leaks and so on.

Install

Just issue from the command line:

> npm install getLastError

Note that this project contains native addons, which are prebuilt for the x86 and x64 versions and included in the package. If you want to rebuild, use:

• Microsoft Visual Studio C++ 2019 (maybe lower, but I didn't test)

Getting started

const ffi = require('ffi-napi');
const getLastError = require("getLastError");

const user32 = ffi.Library("user32.dll", {
	LoadIconA: ["size_t"/* HICON */, [
		"size_t", /* HINSTANCE hInstance  */
		"string", /* LPCSTR    lpIconName */
	]],
	LoadImageA: ["size_t"/* HANDLE */, [
		"size_t", /* HINSTANCE hInst  */
		"string", /* LPCSTR    name   */
		"uint32", /* UINT      type   */
		"int32",  /* int       cx     */
		"int32",  /* int       cy     */
		"uint32", /* UINT      fuLoad */
	]],
});

if (0 === user32.LoadIconA(0, "notExists.ico")) {
	console.log(getLastError(16, true));	// 0x715
}

if (0 === user32.LoadImageA(0, "notExists.ico", IMAGE_ICON = 1, 16, 16, (LR_LOADFROMFILE = 0x10) | (LR_LOADTRANSPARENT = 0x20))) {
	console.log(getLastError(16));	// 2
}

// Do NOT use async, because the `ffi-napi` library will also call some apis that will clear the error.
user32.LoadImageA.async(0, "notExists.ico", IMAGE_ICON, 16, 16, LR_LOADFROMFILE | LR_LOADTRANSPARENT, (err, r) => {
	if (0 === r) {
		console.log("you will never get the correct error code in callback mode:", getLastError(16));
	}
});

API

Syntax

getLastError(base, addPrefix);

Parameters

• base [optional] {number}. Number base(1 ~ 36) of the return value. Defaults to 10.
• addPrefix [optional] {boolean}. Adds 0x if base is 16, 0o if 8, and 0b if 2. Defaults to false.

Returns

Type: string|number

The last error code calling windows api, in the specific number base.