Emscripten

https://emscripten.org
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Emscripten is a complete compiler toolchain to WebAssembly, using LLVM, with a special focus on...
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### Install SDK Target with Specific Tools

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Install an SDK target by explicitly listing all required tools. This provides more granular control over the installed components.

```bash
./emsdk install git-1.8.3 clang-upstream-main-64bit node-0.10.17-64bit python-2.7.5.3-64bit java-7.45-64bit llvm-git-main-64bit emscripten-main-64bit
```

--------------------------------

### Install a Tool or SDK

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Downloads and installs a specified tool or SDK. Replace <tool/sdk> with the target name.

```bash
./emsdk install <tool/sdk>
```

--------------------------------

### Compiling and running Asyncify/JSPI examples

Source: https://emscripten.org/docs/porting/asyncify.html

Commands to compile and execute the Asyncify/JSPI examples.

```bash
emcc -O3 example.cpp -s<ASYNCIFY or JSPI>
```

```bash
node a.out.js
```

```bash
node --experimental-wasm-stack-switching a.out.js
```

--------------------------------

### Quick Toolchain Profiling Example

Source: https://emscripten.org/docs/optimizing/Profiling-Toolchain.html

Run this sequence to get a basic HTML profile of the toolchain's compilation process. Ensure you are in the Emscripten directory and set the EMPROFILE environment variable.

```bash
cd path/to/emscripten
export EMPROFILE=1
emcc test/hello_world.c -O3 -o a.html
emprofile

```

--------------------------------

### Compiling and running async fetch example

Source: https://emscripten.org/docs/porting/asyncify.html

Compilation command for the async fetch example.

```bash
emcc example.c -O3 -o a.html -s<ASYNCIFY or JSPI>
```

--------------------------------

### Install an SDK Target

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Install a predefined SDK target, which bundles a specific release of Emscripten and its associated tools. This is a convenient way to get a complete Emscripten environment.

```bash
./emsdk install sdk-upstream-main-64bit
```

--------------------------------

### Install a Specific Tool or SDK Version

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Downloads and installs a new tool or SDK version by its name.

```bash
./emsdk install <tool/sdk name>
```

```bash
./emsdk install sdk-1.38.21-64bit
```

--------------------------------

### Windows .emscripten Configuration Example

Source: https://emscripten.org/docs/tools_reference/emsdk.html

An example of the .emscripten configuration file on Windows, showing paths to LLVM and Node.js.

```python
# .emscripten file from Windows SDK

import os
LLVM_ROOT='C:/Program Files/Emscripten/clang/e1.21.0_64bit'
NODE_JS='C:/Program Files/Emscripten/node/0.10.17_64bit/node.exe'

```

--------------------------------

### Install and Activate SDK from Main Branch

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Build and activate the Emscripten SDK from the main branch by installing git, cloning the latest emscripten-core/emscripten/main, and setting it as the active version.

```bash
# Install git (Skip if the system already has it).
./emsdk install git-1.8.3

# Clone+pull the latest emscripten-core/emscripten/main.
./emsdk install sdk-main-64bit

# Set this as the active version.
./emsdk activate sdk-main-64bit

```

--------------------------------

### Install and activate tip-of-tree binaries

Source: https://emscripten.org/docs/contributing/developers_guide.html

Use the latest available binaries for testing against the most recent changes.

```bash
emsdk install tot
emsdk activate tot
```

--------------------------------

### Emscripten Fetch Progress and Management Example

Source: https://emscripten.org/docs/api_reference/fetch.html

This example demonstrates how to track download progress using the onprogress callback and manage fetch requests with attributes like request method, load destination, and error/success handlers. It also shows how to initiate a fetch request.

```c
void downloadProgress(emscripten_fetch_t *fetch) {
  if (fetch->totalBytes) {
    printf("Downloading %s.. %.2f%% complete.\n", fetch->url, fetch->dataOffset * 100.0 / fetch->totalBytes);
  } else {
    printf("Downloading %s.. %lld bytes complete.\n", fetch->url, fetch->dataOffset + fetch->numBytes);
  }
}

int main() {
  emscripten_fetch_attr_t attr;
  emscripten_fetch_attr_init(&attr);
  strcpy(attr.requestMethod, "GET");
  attr.attributes = EMSCRIPTEN_FETCH_LOAD_TO_MEMORY;
  attr.onsuccess = downloadSucceeded;
  attr.onprogress = downloadProgress;
  attr.onerror = downloadFailed;
  emscripten_fetch(&attr, "myfile.dat");
}
```

--------------------------------

### Install Latest Emscripten SDK

Source: https://emscripten.org/docs/getting_started/downloads.html

Download and install the latest SDK tools.

```bash
./emsdk install latest
```

--------------------------------

### Linux .emscripten Configuration Example

Source: https://emscripten.org/docs/tools_reference/emsdk.html

An example of the .emscripten configuration file on Linux, specifying Node.js and LLVM root paths.

```python
# .emscripten file from Linux SDK

import os
NODE_JS = 'node'
LLVM_ROOT='/home/ubuntu/emsdk/upstream/bin'

```

--------------------------------

### Install Sphinx dependencies

Source: https://emscripten.org/docs/site/about.html

Use this command to install the required version of Sphinx and other dependencies for building the documentation.

```bash
pip install -r requirements-dev.txt
```

--------------------------------

### Set Binaryen Root Directory

Source: https://emscripten.org/docs/building_from_source/configuring_emscripten_settings.html

Example of how to specify the BINARYEN_ROOT variable within the .emscripten configuration file. Ensure the path points to your Binaryen installation.

```python
BINARYEN_ROOT = 'C:\\tools\\binaryen\\'

```

--------------------------------

### Install MinGW via Emscripten SDK

Source: https://emscripten.org/docs/building_from_source/toolchain_what_is_needed.html

Commands to install and activate the MinGW compiler toolchain using the emsdk utility.

```bash
emsdk install mingw-4.6.2-32bit
emsdk activate mingw-4.6.2-32bit
```

--------------------------------

### Install Emscripten SDK Component

Source: https://emscripten.org/docs/building_from_source/verify_emscripten_environment.html

Install a specific component from the Emscripten SDK repository. Replace 'java-7.45-64bit' with the actual name of the component you need to install.

```bash
./emsdk install java-7.45-64bit

```

--------------------------------

### Use After Free Example

Source: https://emscripten.org/docs/debugging/Sanitizers.html

Demonstrates a heap use-after-free error caught by ASan.

```cpp
int main() {
  int *array = new int[100];
  delete [] array;
  return array[0];
}
```

```bash
$ em++ -gsource-map -fsanitize=address -sALLOW_MEMORY_GROWTH use_after_free.cpp
$ node a.out.js
=================================================================
==42==ERROR: AddressSanitizer: heap-use-after-free on address 0x03203e40 at pc 0x00000c1b bp 0x02965e70 sp 0x02965e7c
READ of size 4 at 0x03203e40 thread T0
    #0 0xc1b in __original_main use_after_free.cpp:4:10
    #1 0xc48 in main+0xc48 (a.out.wasm+0xc48)

0x03203e40 is located 0 bytes inside of 400-byte region [0x03203e40,0x03203fd0)
freed by thread T0 here:
    #0 0x5fe8 in operator delete[](void*)+0x5fe8 (a.out.wasm+0x5fe8)
    #1 0xb76 in __original_main use_after_free.cpp:3:3
    #2 0xc48 in main+0xc48 (a.out.wasm+0xc48)
    #3 0x800019b5 in Object.Module._main a.out.js:6581:32
    #4 0x80001ade in Object.callMain a.out.js:6878:30
    #5 0x80001b18 in doRun a.out.js:6936:60
    #6 0x80001b26 in run a.out.js:6950:5
    #7 0x80001ac9 in runCaller a.out.js:6857:29

previously allocated by thread T0 here:
    #0 0x5db4 in operator new[](unsigned long)+0x5db4 (a.out.wasm+0x5db4)
    #1 0xb41 in __original_main use_after_free.cpp:2:16
    #2 0xc48 in main+0xc48 (a.out.wasm+0xc48)
    #3 0x800019b5 in Object.Module._main a.out.js:6581:32
    #4 0x80001ade in Object.callMain a.out.js:6878:30
    #5 0x80001b18 in doRun a.out.js:6936:60
    #6 0x80001b26 in run a.out.js:6950:5
    #7 0x80001ac9 in runCaller a.out.js:6857:29

SUMMARY: AddressSanitizer: heap-use-after-free (a.out.wasm+0xc1a)
...
```

--------------------------------

### File Content Example

Source: https://emscripten.org/docs/getting_started/Tutorial.html

This is the expected content of the 'test/hello_world_file.txt' file that the C++ code will read.

```text
==
This data has been read from a file.
The file is readable as if it were at the same location in the filesystem, including directories, as in the local filesystem where you compiled the source.
==
```

--------------------------------

### Install Individual Tools or Groups

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Install specific tools or a collection of tools by their identifiers. This can be done for single tools or multiple tools at once.

```bash
./emsdk install node-0.10.17-64bit
```

```bash
./emsdk install node-0.10.17-64bit java-7.45-64bit
```

--------------------------------

### Create Web Audio Context and Start Wasm Audio Worklet Thread

Source: https://emscripten.org/docs/api_reference/wasm_audio_worklets.html

Initializes a Web Audio context and starts an Emscripten Wasm Audio Worklet thread. This is the first step in setting up audio processing with Wasm.

```c
#include <emscripten/webaudio.h>

uint8_t audioThreadStack[4096];

int main()
{
  EMSCRIPTEN_WEBAUDIO_T context = emscripten_create_audio_context(0);

  emscripten_start_wasm_audio_worklet_thread_async(context, audioThreadStack, sizeof(audioThreadStack),
                                                   &AudioThreadInitialized, 0);
}

```

--------------------------------

### Expected output for async fetch example

Source: https://emscripten.org/docs/porting/asyncify.html

The console output observed when running the async fetch example.

```text
before
waiting for a fetch
got the fetch response
after
```

--------------------------------

### Compiling and Running Null Read with UBSan

Source: https://emscripten.org/docs/debugging/Sanitizers.html

Commands to compile and execute the null read example with and without UBSan.

```bash
$ emcc null-read.c
$ node a.out.js
$
```

```bash
$ emcc -fsanitize=undefined null-assign.c
$ node a.out.js
null-read.c:3:9: runtime error: load of null pointer of type 'int'
```

--------------------------------

### Full C++ STL binding example

Source: https://emscripten.org/docs/porting/connecting_cpp_and_javascript/embind.html

A complete example demonstrating C++ functions returning STL containers and their corresponding registration in EMSCRIPTEN_BINDINGS.

```cpp
#include <emscripten/bind.h>
#include <string>
#include <vector>
#include <optional>

using namespace emscripten;

std::vector<int> returnVectorData () {
  std::vector<int> v(10, 1);
  return v;
}

std::map<int, std::string> returnMapData () {
  std::map<int, std::string> m;
  m.insert(std::pair<int, std::string>(10, "This is a string."));
  return m;
}

std::optional<std::string> returnOptionalData() {
  return "hello";
}

EMSCRIPTEN_BINDINGS(module) {
  function("returnVectorData", &returnVectorData);
  function("returnMapData", &returnMapData);
  function("returnOptionalData", &returnOptionalData);

  // register bindings for std::vector<int>, std::map<int, std::string>, and
  // std::optional<std::string>.
  register_vector<int>("vector<int>");
  register_map<int, std::string>("map<int, string>");
  register_optional<std::string>();
}
```

--------------------------------

### Verify Toolchain Installation

Source: https://emscripten.org/docs/building_from_source/toolchain_what_is_needed.html

Standard command-line checks to verify the presence and version of required development tools.

```bash
# Check for Python
python --version

# Check for Node.js
node --version

# Check for Git
git --version

# Check for Java
java -version

# Check for gcc / g++
gcc --version
g++

# Check for cmake
cmake
```

--------------------------------

### Install and Activate Latest Changes with emsdk

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Use 'tot' to install and activate the latest continuously built version of the Emscripten SDK, which includes recent Emscripten and LLVM changes.

```bash
./emsdk install tot
./emsdk activate tot

```

--------------------------------

### Install Git on Linux

Source: https://emscripten.org/docs/getting_started/downloads.html

Install Git on Linux using the system package manager. Git is only required if you intend to use tools from a development branch.

```bash
# Install git
sudo apt-get install git
```

--------------------------------

### Module.preRun / Module.postRun

Source: https://emscripten.org/docs/api_reference/module.html

Lifecycle hooks for executing functions before main() starts or after it returns.

```APIDOC
## Module.preRun / Module.postRun

### Description
- **Module.preRun**: A function or array of functions called after environment setup but before main(). Useful for File System API setup.
- **Module.postRun**: A function or array of functions called after the program's main() returns.
```

--------------------------------

### Installing Emscripten and Make in GitLab CI

Source: https://emscripten.org/docs/compiling/GitLab.html

This section of the .gitlab-ci.yml file details the installation of Emscripten and the 'make' utility from the Alpine Linux testing repository within the 'before_script' stage.

```yaml
before_script:
  - apk add emscripten make --repository=http://dl-cdn.alpinelinux.org/alpine/edge/testing

```

--------------------------------

### Install Tip-of-Tree Emscripten Build

Source: https://emscripten.org/docs/getting_started/downloads.html

Install the latest tip-of-tree build, which represents the most recent code that has passed integration tests. This may be less stable than tagged releases but is useful for testing new features or reporting regressions.

```bash
./emsdk install tot
```

--------------------------------

### Get Help for emsdk

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Displays a list of all supported commands for the emsdk tool.

```bash
./emsdk help
```

--------------------------------

### Example C++ Classes

Source: https://emscripten.org/docs/porting/connecting_cpp_and_javascript/WebIDL-Binder.html

Defines sample C++ classes 'Foo' and 'Bar' with methods and a constructor. These serve as the basis for WebIDL binding.

```cpp
class Foo {
public:
  int getVal();
  void setVal(int v);
};

class Bar {
public:
  Bar(long val);
  void doSomething();
};

```

--------------------------------

### Compiling and Running Null Assignment with UBSan

Source: https://emscripten.org/docs/debugging/Sanitizers.html

Commands to compile and execute the null assignment example with and without UBSan.

```bash
$ emcc null-assign.c
$ node a.out.js
Runtime error: The application has corrupted its heap memory area (address zero)!
```

```bash
$ emcc -fsanitize=undefined null-assign.c
$ node a.out.js
null-assign.c:3:5: runtime error: store to null pointer of type 'int'
Runtime error: The application has corrupted its heap memory area (address zero)!
```

--------------------------------

### Factory constructor usage examples

Source: https://emscripten.org/docs/api_reference/bind.h.html

Various ways to bind a factory function as a class constructor.

```cpp
using namespace std::placeholders;
myClass1.constructor(&my_factory);
myClass2.constructor(std::function<ClassType2(float, float)>(&class2_factory));
myClass3.constructor<ClassType3(const val&)>(std::bind(Class3Functor(), _1));
```

--------------------------------

### Verify Emscripten Installation

Source: https://emscripten.org/docs/getting_started/Tutorial.html

Run this command to verify your Emscripten installation. If you encounter warnings, refer to the debugging guide.

```bash
./emcc -v

```

--------------------------------

### List Available SDKs and Tools

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Lists all currently installed SDKs and tools, along with their status. Use the --old flag to include historical versions.

```bash
./emsdk list
```

```bash
./emsdk list --old
```

--------------------------------

### FS.init(input, output, error)

Source: https://emscripten.org/docs/api_reference/Filesystem-API.html

Sets up standard I/O devices for stdin, stdout, and stderr.

```APIDOC
## FS.init(input, output, error)

### Description
Sets up standard I/O devices for `stdin`, `stdout`, and `stderr` using custom callbacks.

### Parameters
- **input** (function) - Optional - Input callback called when reading from `stdin`.
- **output** (function) - Optional - Output callback called when writing to `stdout`.
- **error** (function) - Optional - Error callback called when writing to `stderr`.
```

--------------------------------

### Emscripten Check Warning Example

Source: https://emscripten.org/docs/building_from_source/verify_emscripten_environment.html

This output indicates a potential issue where the detected LLVM version for clang does not match the expected version. This may require installing or activating the correct LLVM component.

```text
emcc (Emscripten GCC-like replacement + linker emulating GNU ld) 1.21.0
shared:INFO: (Emscripten: Running sanity checks)
emcc: warning: LLVM version for clang executable "/usr/bin/clang" appears incorrect (seeing "16.0", expected "18") [-Wversion-check]

```

--------------------------------

### Synchronous Fetch Example

Source: https://emscripten.org/docs/api_reference/fetch.html

Demonstrates a synchronous GET request to download a file. The emscripten_fetch function blocks until the operation completes. Success and failure callbacks, if provided, are called synchronously before emscripten_fetch returns.

```c
int main() {
  emscripten_fetch_attr_t attr;
  emscripten_fetch_attr_init(&attr);
  strcpy(attr.requestMethod, "GET");
  attr.attributes = EMSCRIPTEN_FETCH_LOAD_TO_MEMORY | EMSCRIPTEN_FETCH_SYNCHRONOUS;
  emscripten_fetch_t *fetch = emscripten_fetch(&attr, "file.dat"); // Blocks here until the operation is complete.
  if (fetch->status == 200) {
    printf("Finished downloading %llu bytes from URL %s.\n", fetch->numBytes, fetch->url);
    // The data is now available at fetch->data[0] through fetch->data[fetch->numBytes-1];
  } else {
    printf("Downloading %s failed, HTTP failure status code: %d.\n", fetch->url, fetch->status);
  }
  emscripten_fetch_close(fetch);
}
```

--------------------------------

### Expected output for sleep example

Source: https://emscripten.org/docs/porting/asyncify.html

The console output observed when running the sleep example.

```text
sleeping...
sleeping...
sleeping...
sleeping...
sleeping...
timer happened!
```

--------------------------------

### Run a local webserver for testing

Source: https://emscripten.org/docs/getting_started/FAQ.html

Use these commands to serve files locally for testing, avoiding issues with file:// URLs.

```bash
python -m http.server
```

```bash
python -m SimpleHTTPServer
```

```bash
emrun FILENAME.html
```

--------------------------------

### List Available SDKs and Tools

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Use the 'list' command to see all available Emscripten SDKs and individual tools.

```bash
./emsdk list
```

--------------------------------

### Mounting a Proxy Filesystem

Source: https://emscripten.org/docs/api_reference/Filesystem-API.html

Demonstrates how to mount one module's filesystem into another using PROXYFS to enable shared access.

```javascript
// Module 2 can use the path "/fs1" to access and modify Module 1's filesystem
module2.FS.mkdir("/fs1");
module2.FS.mount(module2.PROXYFS, {
    root: "/",
    fs: module1.FS
}, "/fs1");
```

--------------------------------

### Install and Activate Old Emscripten SDK Version

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Installs and activates a specific archived tool or SDK version.

```bash
# Install the required version.
./emsdk install <name_of_tool>

# Activate required version.
./emsdk activate <name_of_tool>
```

--------------------------------

### Install specific Emscripten build

Source: https://emscripten.org/docs/contributing/developers_guide.html

Use this command to install a specific build of Emscripten identified by its commit hash.

```bash
emsdk install [HASH]
```

--------------------------------

### Install a Specific Emscripten SDK Version

Source: https://emscripten.org/docs/getting_started/downloads.html

Install a specific tagged release of the Emscripten SDK by providing the version number.

```bash
./emsdk install 1.38.45
```

--------------------------------

### SDL Hello World C Code with Emscripten Integration

Source: https://emscripten.org/docs/getting_started/Tutorial.html

This C code demonstrates a basic SDL application that initializes video, draws a colored square, and prints output. It includes Emscripten-specific includes and macros for potential browser integration.

```c
// Copyright 2011 The Emscripten Authors.  All rights reserved.
// Emscripten is available under two separate licenses, the MIT license and the
// University of Illinois/NCSA Open Source License.  Both these licenses can be
// found in the LICENSE file.

#include <stdio.h>
#include <SDL/SDL.h>

#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#endif

int main(int argc, char** argv) {
  printf("Hello, world!\n");

  SDL_Init(SDL_INIT_VIDEO);
  SDL_Surface *screen = SDL_SetVideoMode(256, 256, 32, SDL_SWSURFACE);

#ifdef TEST_SDL_LOCK_OPTS
  EM_ASM("SDL.defaults.copyOnLock = false; SDL.defaults.discardOnLock = true; SDL.defaults.opaqueFrontBuffer = false;");
#endif

  if (SDL_MUSTLOCK(screen)) SDL_LockSurface(screen);
  for (int i = 0; i < 256; i++) {
    for (int j = 0; j < 256; j++) {
#ifdef TEST_SDL_LOCK_OPTS
      // Alpha behaves like in the browser, so write proper opaque pixels.
      int alpha = 255;
#else
      // To emulate native behavior with blitting to screen, alpha component is ignored. Test that it is so by outputting
      // data (and testing that it does get discarded)
      int alpha = (i+j) % 255;
#endif
      *((Uint32*)screen->pixels + i * 256 + j) = SDL_MapRGBA(screen->format, i, j, 255-i, alpha);
    }
  }
  if (SDL_MUSTLOCK(screen)) SDL_UnlockSurface(screen);
  SDL_Flip(screen);

  printf("you should see a smoothly-colored square - no sharp lines but the square borders!\n");
  printf("and here is some text that should be HTML-friendly: amp: |&| double-quote: |\"| quote: |'| less-than, greater-than, html-like tags: |<cheez></cheez>|\nanother line.\n");

  SDL_Quit();

  return 0;
}

```

--------------------------------

### Instantiate a Modularized Module

Source: https://emscripten.org/docs/tools_reference/settings_reference.html

Demonstrates how to instantiate a module when MODULARIZE is enabled using either async/await or promise-based syntax.

```javascript
const module = await EXPORT_NAME();
```

```javascript
let module;
EXPORT_NAME().then(instance => {
  module = instance;
});
```

--------------------------------

### Install Emscripten SDK Asserts Version

Source: https://emscripten.org/docs/tools_reference/emsdk.html

Installs and activates a specific 'asserts' version of the Emscripten SDK, which includes more runtime checks.

```bash
./emsdk install 4.0.7-asserts
./emsdk activate 4.0.7-asserts
```

--------------------------------

### Create and Run a Wasm Worker

Source: https://emscripten.org/docs/api_reference/wasm_workers.html

This example demonstrates creating a Wasm Worker and posting a function to execute within it. Ensure to build with the `-sWASM_WORKERS` flag.

```c
#include <emscripten/wasm_worker.h>
#include <stdio.h>

void run_in_worker()
{
  printf("Hello from Wasm Worker!\n");
}

int main()
{
  emscripten_wasm_worker_t worker = emscripten_malloc_wasm_worker(/*stackSize: */4096);
  emscripten_wasm_worker_post_function_v(worker, run_in_worker);
}
```

--------------------------------

### Creating a Directory Tree

Source: https://emscripten.org/docs/api_reference/Filesystem-API.html

Creates a directory and all necessary parent directories.

```javascript
FS.mkdirTree('/data/subdir1/subdir2');
```

--------------------------------

### Install Compiler Toolchain on Linux

Source: https://emscripten.org/docs/building_from_source/toolchain_what_is_needed.html

Commands to install the build-essential package for GCC and the CMake build system on Debian-based Linux distributions.

```bash
# Install gcc
sudo apt-get install build-essential
# Install cmake
sudo apt-get install cmake
```

--------------------------------

### Build Basic C++ Example with Emscripten

Source: https://emscripten.org/docs/building_from_source/verify_emscripten_environment.html

Compile a simple C++ file using Emscripten to verify the build process. This command should complete without warnings, producing an output JavaScript file.

```bash
cd emscripten/<version of emscripten you installed>
./emcc test/hello_world.cpp

```

--------------------------------

### Install and activate CI-verified emsdk binaries

Source: https://emscripten.org/docs/contributing/developers_guide.html

Use the version specified in the repository's test configuration to ensure compatibility with the test suite.

```bash
emsdk install $(cat test/emsdk_version.txt)
emsdk activate $(cat test/emsdk_version.txt)
```

--------------------------------

### Applying Per-File Optimizations

Source: https://emscripten.org/docs/compiling/Building-Projects.html

Shows how to apply different optimization levels to specific source files before linking.

```bash
# Optimize the first file for size, and the rest using `-O2`.
emcc -Oz a.cpp -c -o a.o
emcc -O2 b.cpp -c -o b.o
emcc -O2 a.o b.o -o project.js
```

--------------------------------

### EVAL_CTORS Logging Example (Partial Success)

Source: https://emscripten.org/docs/optimizing/Optimizing-Code.html

Example output when EVAL_CTORS partially succeeds but stops due to an import call (e.g., reading from environment). This indicates areas where optimization was limited.

```text
trying to eval __wasm_call_ctors
  ...partial evalling successful, but stopping since could not eval: call import: wasi_snapshot_preview1.environ_sizes_get
       recommendation: consider --ignore-external-input
  ...stopping

```

--------------------------------

### Applying Optimization Flags

Source: https://emscripten.org/docs/compiling/Building-Projects.html

Demonstrates sub-optimal and recommended practices for applying optimization flags during compilation and linking.

```bash
# Sub-optimal - JavaScript/WebAssembly optimizations are omitted
emcc -O2 a.cpp -c -o a.o
emcc -O2 b.cpp -c -o b.o
emcc a.o b.o -o project.js

# Sub-optimal - LLVM optimizations omitted
emcc a.cpp -c -o a.o
emcc b.cpp -c -o b.o
emcc -O2 a.o b.o -o project.js

# Usually the right thing: The same options are provided at compile and link.
emcc -O2 a.cpp -c -o a.o
emcc -O2 b.cpp -c -o b.o
emcc -O2 a.o b.o -o project.js
```

--------------------------------

### Install Python and CMake on Linux

Source: https://emscripten.org/docs/getting_started/downloads.html

Install Python and CMake using the system package manager on Linux. Python is required by emsdk, and CMake is optional but needed for tests and building certain components.

```bash
sudo apt-get install python3

# Install CMake (optional, only needed for tests and building Binaryen or LLVM)
sudo apt-get install cmake
```

--------------------------------

### Using VoidPtr and any for void*

Source: https://emscripten.org/docs/porting/connecting_cpp_and_javascript/WebIDL-Binder.html

Describes how `void*` is handled using `VoidPtr` (behaves like a pointer wrapper) or `any` (behaves like a 32-bit integer) in IDL files.

```text
The `void*` type is supported through a `VoidPtr` type that you can use in IDL files. You can also use the `any` type.
The difference between them is that `VoidPtr` behaves like a pointer type in that you get a wrapper object, while `any` behaves like a 32-bit integer (which is what raw pointers are in Emscripten-compiled code).
```

--------------------------------

### EVAL_CTORS Logging Example (Success with main() Stop)

Source: https://emscripten.org/docs/optimizing/Optimizing-Code.html

Example output when EVAL_CTORS successfully evaluates global constructors but stops during main() evaluation due to an import call (e.g., writing to file descriptor).

```text
trying to eval __wasm_call_ctors
  ...success on __wasm_call_ctors.
trying to eval main
  ...stopping (in block) since could not eval: call import: wasi_snapshot_preview1.fd_write
  ...stopping

```

--------------------------------

### FS.cwd()

Source: https://emscripten.org/docs/api_reference/Filesystem-API.html

Gets the current working directory.

```APIDOC
## FS.cwd()

### Description
Gets the current working directory.

### Returns
- **path** (string) - The current working directory.
```

--------------------------------

### Standard Autoconf Build Commands

Source: https://emscripten.org/docs/compiling/Building-Projects.html

Typical commands used to build a project based on configure and make.

```bash
./configure
make
```

--------------------------------

### FS.getPath(node)

Source: https://emscripten.org/docs/api_reference/Filesystem-API.html

Gets the absolute path to a node.

```APIDOC
## FS.getPath(node)

### Description
Gets the absolute path to node, accounting for mounts.

### Parameters
- **node** (object) - Required - The current node.

### Returns
- **path** (string) - The absolute path to node.
```

--------------------------------

### Display test runner help

Source: https://emscripten.org/docs/getting_started/test-suite.html

View available options and commands for the test runner.

```bash
test/runner --help
```

--------------------------------

### iterable

Source: https://emscripten.org/docs/api_reference/bind.h.html

Makes a bound class iterable in JavaScript by installing Symbol.iterator.

```APIDOC
## iterable

### Description
Enables iteration over a bound class in JavaScript by installing `Symbol.iterator`. This allows the class to be used with `for...of` loops, `Array.from()`, and spread syntax.

### Signature
`template<typename ElementType> const class_& iterable(const char* sizeMethodName, const char* getMethodName) const`

### Parameters
- **sizeMethodName** (const char*) - The name of the method that returns the size of the collection.
- **getMethodName** (const char*) - The name of the method that retrieves an element by index.
```

--------------------------------

### Run tests with fail-fast and start-at options

Source: https://emscripten.org/docs/getting_started/test-suite.html

Use --failfast to stop on the first error and --start-at to resume testing from a specific point. This is most effective when running tests serially.

```bash
test/runner browser --start-at test_foo --failfast
```

--------------------------------

### emscripten_trace_record_frame_start

Source: https://emscripten.org/docs/api_reference/trace.h.html

Records the start of a new frame or event loop iteration.

```APIDOC
## emscripten_trace_record_frame_start

### Description
Records the beginning of a new frame or an iteration of the application's main event loop. This is useful for analyzing frame-based performance.
```

--------------------------------

### Activate Latest Emscripten SDK

Source: https://emscripten.org/docs/getting_started/downloads.html

Set up the compiler configuration to point to the 'latest' SDK.

```bash
./emsdk activate latest
```

--------------------------------

### emscripten_get_element_css_size

Source: https://emscripten.org/docs/api_reference/html5.h.html

Gets the current CSS width and height of a specified element.

```APIDOC
## emscripten_get_element_css_size

### Description
Gets the current CSS width and height of the element specified by target.

### Parameters
- **target** (const char*) - Required - Element to get size of.
- **width** (double*) - Required - Pointer to store width.
- **height** (double*) - Required - Pointer to store height.

### Returns
- **EMSCRIPTEN_RESULT** - Returns EMSCRIPTEN_RESULT_SUCCESS or other result values.
```

--------------------------------

### Configure pre-compressed WebAssembly files

Source: https://emscripten.org/docs/compiling/WebAssembly.html

Enables content negotiation for pre-compressed .wasm.gz files to reduce server CPU load.

```apache
Options Multiviews
RemoveType .gz
AddEncoding x-gzip .gz
AddType application/wasm .wasm
```

--------------------------------

### Window Title Functions

Source: https://emscripten.org/docs/api_reference/emscripten.h.html

Functions to get and set the browser window title.

```APIDOC
## char *emscripten_get_window_title()

### Description
Returns the current window title.

## void emscripten_set_window_title(char *title)

### Description
Sets the browser window title.

### Parameters
- **title** (char *) - Required - The new title string.
```

--------------------------------

### Compile C and C++ with WebAssembly EH and setjmp-longjmp

Source: https://emscripten.org/docs/porting/setjmp-longjmp.html

Example of compiling C and C++ files separately, ensuring consistent WebAssembly EH and setjmp-longjmp support, before linking them together.

```bash
emcc -c -sSUPPORT_LONGJMP=wasm a.c -o a.o
em++ -c -fwasm-exceptions b.cpp -o b.o
em++ -fwasm-exceptions a.o b.o -o test.js
```

--------------------------------

### Get Downcaster prototype

Source: https://emscripten.org/docs/api_reference/bind.h.html

Prototype for the static method to retrieve a downcaster function.

```cpp
//prototype
template<typename ClassType>
static Downcaster<ClassType> getDowncaster()
```

--------------------------------

### FS.mkdev

Source: https://emscripten.org/docs/api_reference/Filesystem-API.html

Creates a new device node in the file system.

```APIDOC
## FS.mkdev(path, mode, dev)

### Description
Creates a new device node in the file system referencing the registered device driver for dev.

### Parameters
- **path** (string) - Required - The path name for the new device node.
- **mode** (int) - Optional - File permissions for the new node. Default is 0777.
- **dev** (int) - Required - The registered device driver.
```

--------------------------------

### Get Upcaster prototype

Source: https://emscripten.org/docs/api_reference/bind.h.html

Prototype for the static method to retrieve an upcaster function.

```cpp
//prototype
template<typename ClassType>
static Upcaster<ClassType> getUpcaster()
```

--------------------------------

### Pass Configuration to Factory Function

Source: https://emscripten.org/docs/tools_reference/settings_reference.html

Shows how to provide default values to the module instance during instantiation.

```javascript
const module = await EXPORT_NAME({ option: value, ... });
```
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