Loading dynamic link libraries in JavaScript
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jswin - Loading dynamic link libraries in JavaScript

jswin is a simple runtime environment based on Google V8 that allows calling functions in DLLs from pure JavaScript. The functions must follow the stdcall or cdecl calling convention. Arguments must be supplied as C compatible data types, such as integers or structs (JavaScript Typed Arrays). Strings are automatically converted to UTF-8. JavaScript functions can be converted to function pointers callable from C code in the library.


Loading a DLL and calling a function with multiple arguments:

var user32 = loadLibrary("user32.dll");
var MessageBox = user32.getProc("MessageBoxA", "icci", "stdcall");
MessageBox(0, "Hello World!", "Info", 0);

Using callback functions:

var onMouseDownHandler = new CallbackFunction("ii", "stdcall", function(x, y) {
    // ...

var SetOnMouseDownHandler = ....

API Reference

loadLibrary(dllName) returns DLLObject

Loads the library with the given name.

getBaseAddress(array) returns number

Returns the base address of an ArrayBuffer. This is the memory address of the first element in the array. The address remains valid as long as the ArrayBuffer is not deleted by the garbage collector.


Terminates the process. Set status to 0 to indicate success. Use another status code to indicate failure.

DLLObject.getProc(procName, signature, callingConvention[, returnType]) returnsDLLProc`

Retrieves the function named procName from the DLL. When calling the function from JavaScript, the arguments are converted as specified in signature. callingConvention must be "stdcall" or "cdecl". The returned value is converted according to returnType. If returnTypeis not given, i is assumed.

signature is a string in which each character specifies the C compatible type of an argument. The following types are supported:

  • i integer
  • u unsigned integer
  • c ANSI string
  • w wide character string
  • s struct or array

returnType is a string with length 1. The following types are supported:

  • i integer
  • u unsigned integer
  • v void (function returns undefined)

JavaScript strings are converted to UTF-8 encoded, null-terminated byte arrays (C strings). Structs or arrays have to be supplied as ArrayBuffer. Passing null instead of string or array is converted to NULL pointer.

DLLProc(...) returns number

Calls the function of the corresponding DLL. The result of the function is returned as an integer.

new DLLProc(signature, callingConvention, address) returns number

Constructs a new object describing a function callable from C. signature and callingConvention are identical to DLLObject.getProc(...). address is the memory address of the function. Usually, instances of DLLProc are constructed by calling DLLObject.getProc(...) instead of using this constructor function.

DLLProc.getAddress() returns number

Returns the address of the function corresponding to the DLLProc object.

new CallbackFunction(signature, callingConvention, func[, returnType]) returns CallbackFunction

Constructs a new object describing a JavaScript function callable from C. signature, callingConvention, and returnType are identical to DLLObject.getProc(...). func is a JavaScript function.

Allowed argument types for signature: i, u Allowed return types: i, u, v

CallbackFunction.getAddress() returns number

Returns a C compatible address for the JavaScript function corresponding to the CallbackFunction object. This address can be passed as argument when calling a function from the DLL. The address remains valid as long as the CallbackFunction is not deleted by the garbage collector.

require(moduleId) returns Object

Loads and executes code in another JavaScript file. Based on CommonJS Modules 1.1.1.

fromMemory(address, byteLength) returns Object

Constructs an ArrayBuffer over an existing memory block with length byteLength at address. The buffer does not take ownership of the memory, which means that deleting the buffer by the garbage collector does not free the memory.

readString(type, address) returns String

Copies a null-terminated C string stored in memory at address into a JavaScript string. type has to be one of the following:

  • c ANSI string
  • w wide character string

Building self-running executables

jswin_wrapper wraps JavaScript code in a Windows executable (.exe) for easy distribution. The JavaScript modules are bundled with a loader application (jswin_loader) which runs the main module at startup. jswin resides in a DLL (jswinrt.dll) to be shared by multiple executables.


This source code package contains project files for Microsoft Visual C++ 2012.


  • Google V8, Version 3.22.15 or compatible


MIT License