Hi @kleisauke ,
I am trying the same on my local machine but getting the same error not rechable , so Do I have to run specific function before running vips_init(),
Now I am trying to achieve the same in local environment with node.js and express server.

Visit http://localhost:3000/init-vips to initialize the Vips module WASM module loaded successfully Available exports: [ '__getTypeName', '_embind_initialize_bindings', '__wasm_call_ctors', 'vips_init', 'get_vips_version', 'strerror', '__indirect_function_table', 'free', 'malloc', 'ntohs', '_emscripten_tls_init', 'pthread_self', '_initialize', '_emscripten_thread_init', '_emscripten_thread_crashed', 'emscripten_main_thread_process_queued_calls', 'htons', 'htonl', 'emscripten_main_runtime_thread_id', 'emscripten_stack_get_base', 'emscripten_stack_get_end', '_emscripten_run_on_main_thread_js', '_emscripten_thread_free_data', '_emscripten_thread_exit', 'emscripten_get_sbrk_ptr', 'sbrk', '_emscripten_check_mailbox', 'setThrew', '_emscripten_tempret_set', 'emscripten_stack_init', 'emscripten_stack_set_limits', 'emscripten_stack_get_free', '_emscripten_stack_restore', '_emscripten_stack_alloc', 'emscripten_stack_get_current', '__cxa_demangle', '__cxa_free_exception', '__cxa_increment_exception_refcount', '__cxa_decrement_exception_refcount', '__get_exception_message', '__cxa_can_catch', '__cxa_is_pointer_type', '__set_stack_limits' ] Calling __wasm_call_ctors _emscripten_init_main_thread_js called Error during WebAssembly instantiation: RuntimeError: unreachable at wasm://wasm/010ec636:wasm-function[7568]:0x2d9813 at wasm://wasm/010ec636:wasm-function[7831]:0x2e25a5 at wasm://wasm/010ec636:wasm-function[7504]:0x2d7398 at wasm://wasm/010ec636:wasm-function[59]:0x510a at safeCall (file:///Users/rahul/projects/nodeprojects/wasm-node-express-project/server.js:18:29) at loadWasmModule (file:///Users/rahul/projects/nodeprojects/wasm-node-express-project/server.js:191:5) at async file:///Users/rahul/projects/nodeprojects/wasm-node-express-project/server.js:210:27

Do I have to run specific function in order to initiliaze the vips_init ? 

vips-es6.js , vips-es6.wasm works fine with index.html, or react but when I am trying to load the vips0es6.wasm in node the wasm module is loading but the moment I am trying to call vips_init I am having error unreachable,

Do I have to call the following

__wasm_call_ctors'
_emscripten_tls_init'
'_initialize'

Please share your thoughs for this

I would start by removing these debug and instrumentation flags:

-sASSERTIONS=2 --threadprofiler -sSAFE_HEAP=1 -sCHECK_NULL_WRITES=0 -sLIBRARY_DEBUG -sEXCEPTION_DEBUG -sSYSCALL_DEBUG -sDYLINK_DEBUG -sSTACK_OVERFLOW_CHECK=2 -sRUNTIME_DEBUG=1

Additionally, note that -sSTANDALONE_WASM is incompatible with Emscripten's current pthread integration, as thread creation requires JavaScript support.

Hello @kleisauke,

Following your suggestion, I have removed the debug flag and added -sUSE_PTHREADS=0. In Node.js, i am creating multiple workers, each loading the Vips module, which subsequently creates threads.

Here is the C++ function _generate_small_image, which is responsible for generating the small image:

Worker 7 Status:

Worker 7 is ready.
Vips WASM module initialized.
Vips instance within worker: Object [ 'incrementExceptionRefcount', 'decrementExceptionRefcount', 'getExceptionMessage', 'BindingError', 'InternalError', 'count_emval_handles', 'getInheritedInstanceCount', 'getLiveInheritedInstances', 'setAutoDeleteLater', 'flushPendingDeletes', 'setDelayFunction', '_generate_small_image', '_malloc', '_free', '_free_result', '__initialize', 'bigintToI53Checked', 'ENV', 'ccall', 'cwrap', 'addFunction', 'UTF8ToString', 'stringToNewUTF8', 'FS', 'allocateUTF8', 'deletionQueue', 'HEAP8', 'HEAP16', 'HEAPU8', 'HEAPU16', 'HEAP32', 'HEAPU32', 'HEAPF32', 'HEAPF64', 'HEAP64', 'HEAPU64', 'calledRun', 'stdin', 'stdout', 'stderr' ]
Thread "Thread 1" (0x00000001) is now running.
However, when attempting to call generate_small_image via a POST method in Node.js, I encountered the following error

About to call generate_small_image generate_small_image completed Raw result: Error: VIPS error - glib: Error creating thread: Resource temporarily unavailable glib: Error creating thread: Resource temporarily unavailable

And here is my CPP code just for the reference , Its very basic
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <vips/vips.h>

extern "C" {

char* generate_small_image() {
char* result = nullptr;
VipsImage* image = nullptr;
void* buffer = nullptr;
size_t buffer_size = 0;
char* base64 = nullptr;

if (VIPS_INIT("generate_small_image")) {
    return strdup("Error: VIPS initialization failed");
}

// Create a simple colored image (red)
unsigned char* data = (unsigned char*)malloc(200 * 100 * 3);
if (!data) {
    result = strdup("Error: Failed to allocate memory for image data");
    goto cleanup;
}
for (int i = 0; i < 200 * 100 * 3; i += 3) {
    data[i] = 255;  // Red
    data[i+1] = 0;  // Green
    data[i+2] = 0;  // Blue
}

image = vips_image_new_from_memory(data, 200 * 100 * 3, 200, 100, 3, VIPS_FORMAT_UCHAR);
if (!image) {
    result = strdup("Error: Failed to create image");
    goto cleanup;
}

// Write the image to a buffer as PNG
if (vips_pngsave_buffer(image, &buffer, &buffer_size, nullptr)) {
    result = strdup("Error: Failed to save image to buffer");
    goto cleanup;
}

// Encode the buffer as base64
base64 = g_base64_encode((const guchar*)buffer, buffer_size);
if (!base64) {
    result = strdup("Error: Failed to encode image to base64");
    goto cleanup;
}

// Create the result string
result = (char*)malloc(strlen(base64) + 50); // Extra space for JSON formatting
if (!result) {
    result = strdup("Error: Memory allocation failed for result");
    goto cleanup;
}

sprintf(result, "{\"image\":\"%s\"}", base64);

cleanup:
if (data) free(data);
if (image) g_object_unref(image);
if (buffer) g_free(buffer);
if (base64) g_free(base64);

const char* vips_error = vips_error_buffer();
if (vips_error && *vips_error) {
    char* error_result = (char*)malloc(strlen(vips_error) + 50);
    if (error_result) {
        sprintf(error_result, "Error: VIPS error - %s", vips_error);
        if (result) free(result);
        result = error_result;
    }
}

vips_thread_shutdown();
vips_error_clear();

return result ? result : strdup("Error: Unknown error occurred");

}

void free_result(char* ptr) {
free(ptr);
}

}

This works fine in index.html react (browser) , but with node.js it's not though while compiling I do have vips-node.js , vips-node.wasm files.

If you have any insights on how to resolve this thread creation issue or if additional adjustments are needed, your guidance would be greatly appreciated. Thank you!

My basic need is , I have a C++ code and which process the images, I have compiled the code to WASM and it works fine with react but my main purpose is I want to create an API which will load the wasm module and that exported function, and that function I can use in (cloudflare worker or from any other framework
)

[...] and added -sUSE_PTHREADS=0

Please remove this flag. As I said in the linked issue, wasm-vips requires threading functionality to be available, so it must be compiled and linked with the -pthread flag to work correctly.