What languages are supported?

WebAssembly's high-level goals for their MVP was to provide roughly the same functionality as asm.js. The two technologies are very closely related. C, C++, and Rust are very popular languages that support manual memory allocation, which made them ideal candidates for the initial implementation. In this section, we're going to provide a brief overview of each programming language.

C and C++

C and C++ are low-level programming languages that have been around for over 30 years. C is procedural and doesn't inherently support object-oriented programming concepts such as classes and inheritance, but it's fast, portable, and widely used. 

C++ was built to fill the gaps in C by adding features such as operator overloading and improved type checking. Both languages consistently rank in the top 10 most popular programming languages, which make them ideally suited for the MVP:

TIOBE Very Long Term History of the top 10 programming languages

C and C++ support is also baked into Emscripten, so in addition to simplifying the compilation process, it allows you to take advantage of WebAssembly's full capabilities. It is also possible to compile C/C++ code down to a .wasm file using LLVM. LLVM is a collection of modular and reusable compiler and toolchain technologies. In a nutshell, it's a framework that simplifies the configuration of a compilation process from source code to machine code. If you made your own programming language and would like to build a compiler, LLVM has tools to simplify the process. I'll cover how to compile C/C++ into .wasm files using LLVM in Chapter 10, Advanced Tools and Upcoming Features.

The following snippet demonstrates how to print Hello World! to the console using C++:

#include <iostream>

int main() {
    std::cout << "Hello, World!\n";
    return 0;
}

Rust

C and C++ were intended to be the primary languages used for WebAssembly, but Rust is a perfectly suitable substitute. Rust is a systems programming language that is syntactically similar to C++. It was designed with memory safety in mind, but still retains the performance advantages of C and C++. The current nightly build of Rust's compiler can generate .wasm files from Rust source code, so if you prefer Rust and are familiar with C++, you should be able to use Rust for most of the examples in this book.

The following snippet demonstrates how to print Hello World! to the console using Rust:

fn main() {
    println!("Hello World!");
}

Other languages

Various tooling exists to enable the use of WebAssembly with some of the other popular programming languages, although they are mostly experimental:

• C# via Blazor
• Haxe via WebIDL
• Java via TeaVM or Bytecoder
• Kotlin via TeaVM
• TypeScript via AssemblyScript

It is also technically possible to transpile a language to C and consequently compile that to a Wasm module, but the success of compilation is contingent on the output of the transpiler. More than likely, you'd have to make significant changes to the code to get it to work.