# `wasmer` [](https://github.com/wasmerio/wasmer/actions?query=workflow%3Abuild) [](https://slack.wasmer.io) [](https://github.com/wasmerio/wasmer/blob/master/LICENSE) [](https://crates.io/crates/wasmer)
[`Wasmer`](https://wasmer.io/) is the most popular
[WebAssembly](https://webassembly.org/) runtime for Rust. It supports
JIT (Just In Time) and AOT (Ahead Of Time) compilation as well as
pluggable compilers suited to your needs.
It's designed to be safe and secure, and runnable in any kind of environment.
## Usage
Here is a small example of using Wasmer to run a WebAssembly module
written with its WAT format (textual format):
```rust
use wasmer::{Store, Module, Instance, Value, imports};
fn main() -> anyhow::Result<()> {
let module_wat = r#"
(module
(type $t0 (func (param i32) (result i32)))
(func $add_one (export "add_one") (type $t0) (param $p0 i32) (result i32)
get_local $p0
i32.const 1
i32.add))
"#;
let mut store = Store::default();
let module = Module::new(&store, &module_wat)?;
// The module doesn't import anything, so we create an empty import object.
let import_object = imports! {};
let instance = Instance::new(&mut store, &module, &import_object)?;
let add_one = instance.exports.get_function("add_one")?;
let result = add_one.call(&mut store, &[Value::I32(42)])?;
assert_eq!(result[0], Value::I32(43));
Ok(())
}
```
[Discover the full collection of examples](https://github.com/wasmerio/wasmer/tree/master/examples).
## Features
Wasmer is not only fast, but also designed to be *highly customizable*:
* **Pluggable compilers** — A compiler is used by the engine to
transform WebAssembly into executable code:
* [`wasmer-compiler-singlepass`] provides a fast compilation-time
but an unoptimized runtime speed,
* [`wasmer-compiler-cranelift`] provides the right balance between
compilation-time and runtime performance, useful for development,
* [`wasmer-compiler-llvm`] provides a deeply optimized executable
code with the fastest runtime speed, ideal for production.
* **Headless mode** — Once a WebAssembly module has been compiled, it
is possible to serialize it in a file for example, and later execute
it with Wasmer with headless mode turned on. Headless Wasmer has no
compiler, which makes it more portable and faster to load. It's
ideal for constrainted environments.
* **Cross-compilation** — Most compilers support cross-compilation. It
means it possible to pre-compile a WebAssembly module targetting a
different architecture or platform and serialize it, to then run it
on the targetted architecture and platform later.
* **Run Wasmer in a JavaScript environment** — With the `js` Cargo
feature, it is possible to compile a Rust program using Wasmer to
WebAssembly. In this context, the resulting WebAssembly module will
expect to run in a JavaScript environment, like a browser, Node.js,
Deno and so on. In this specific scenario, there is no engines or
compilers available, it's the one available in the JavaScript
environment that will be used.
Wasmer ships by default with the Cranelift compiler as its great for
development purposes. However, we strongly encourage to use the LLVM
compiler in production as it performs about 50% faster, achieving
near-native speeds.
Note: if one wants to use multiple compilers at the same time, it's
also possible! One will need to import them directly via each of the
compiler crates.
Read [the documentation to learn
more](https://wasmerio.github.io/wasmer/crates/doc/wasmer/).
---
Made with ❤️ by the Wasmer team, for the community
[`wasmer-compiler-singlepass`]: https://github.com/wasmerio/wasmer/tree/master/lib/compiler-singlepass
[`wasmer-compiler-cranelift`]: https://github.com/wasmerio/wasmer/tree/master/lib/compiler-cranelift
[`wasmer-compiler-llvm`]: https://github.com/wasmerio/wasmer/tree/master/lib/compiler-llvm