3 unstable releases

0.18.0 Jul 20, 2021
0.18.0-pre.1 Jul 9, 2021
0.17.1 Oct 28, 2020

#526 in WebAssembly

Download history 1258/week @ 2022-12-03 1143/week @ 2022-12-10 934/week @ 2022-12-17 426/week @ 2022-12-24 452/week @ 2022-12-31 1060/week @ 2023-01-07 1199/week @ 2023-01-14 1646/week @ 2023-01-21 1395/week @ 2023-01-28 1546/week @ 2023-02-04 1379/week @ 2023-02-11 1508/week @ 2023-02-18 942/week @ 2023-02-25 1292/week @ 2023-03-04 1112/week @ 2023-03-11 1262/week @ 2023-03-18

4,773 downloads per month

MIT license

16K SLoC

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Wasmer Runtime

Wasmer is a standalone JIT WebAssembly runtime, aiming to be fully compatible with Emscripten, Rust and Go. Learn more.

This crate represents the high-level runtime API, making embedding WebAssembly in your application easy, efficient, and safe.

How to use Wasmer Runtime

The easiest way is to use the instantiate function to create an Instance. Then you can use call or func and then call to call an exported function safely.


Given this WebAssembly:

  (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

compiled into Wasm bytecode, we can call the exported add_one function:

static WASM: &'static [u8] = &[
    // The module above compiled to bytecode goes here.
    0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x06, 0x01, 0x60,
    0x01, 0x7f, 0x01, 0x7f, 0x03, 0x02, 0x01, 0x00, 0x07, 0x0b, 0x01, 0x07,
    0x61, 0x64, 0x64, 0x5f, 0x6f, 0x6e, 0x65, 0x00, 0x00, 0x0a, 0x09, 0x01,
    0x07, 0x00, 0x20, 0x00, 0x41, 0x01, 0x6a, 0x0b, 0x00, 0x1a, 0x04, 0x6e,
    0x61, 0x6d, 0x65, 0x01, 0x0a, 0x01, 0x00, 0x07, 0x61, 0x64, 0x64, 0x5f,
    0x6f, 0x6e, 0x65, 0x02, 0x07, 0x01, 0x00, 0x01, 0x00, 0x02, 0x70, 0x30,

use wasmer_runtime::{

fn main() -> error::Result<()> {
    // We're not importing anything, so make an empty import object.
    let import_object = imports! {};

    let instance = instantiate(WASM, &import_object)?;

    let values = instance

    assert_eq!(values[0], Value::I32(43));

Additional Notes

The wasmer-runtime crate is built to support multiple compiler backends. We support having a Cranelift backend in the wasmer-clif-backend crate, a LLVM backend in the [wasmer-llvm-backend] crate, and the Singlepass backend in the [wasmer-singlepass-backend] crate. Currently, the Cranelift backend is the default.

You can specify the compiler you wish to use with the compile_with function.


~254K SLoC