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Quickstart for JavaScript


Install WasmEdge

Clone the wasmedge-quickjs repo and use it as the current directory.

git clone
cd wasmedge-quickjs

Then download the pre-built WasmEdge QuickJS Runtime program, and optionally, AOT compile it for better performance.

curl -OL
wasmedge compile wasmedge_quickjs.wasm wasmedge_quickjs.wasm

The reason to use wasmedge-quickjs as the current working directory is that modules in the repo are required for the QuickJS runtime.

Quick start

You can try a simple "hello world" JavaScript program (example_js/hello.js), which prints out the command line arguments to the console.

$ wasmedge --dir .:. wasmedge_quickjs.wasm example_js/hello.js WasmEdge Runtime
Hello WasmEdge Runtime

The --dir .:. on the command line is to give wasmedge permission to read the local directory in the file system for the hello.js file.

The JavaScript source code for the hello.js program is as follows.

import * as os from 'os';
import * as std from 'std';

args = args.slice(1);
print('Hello', ...args);
setTimeout(() => {
print('timeout 2s');
}, 2000);

Build it yourself

This section is optional. Read on if you are interested in adding custom built-in JavaScript APIs to the runtime.

Following the instructions, you can build a JavaScript interpreter for WasmEdge. Make sure you have installed GCC. If you don't, run the following command line.

# Install GCC
sudo apt update
sudo apt install build-essential

Then, we could build the WasmEdge-Quickjs runtime.

Fork or clone the wasmedge-quickjs Github repository.

# get the source code
git clone
cd wasmedge-quickjs

# Build the QuickJS JavaScript interpreter
cargo build --target wasm32-wasi --release

The WebAssembly-based JavaScript interpreter program is located in the build target directory.

WasmEdge provides a wasmedgec utility to compile and add a native machine code section to the wasm file. You can use wasmedge to run the natively instrumented wasm file to get a much faster performance.

wasmedge compile target/wasm32-wasi/release/wasmedge_quickjs.wasm wasmedge_quickjs.wasm
wasmedge --dir .:. wasmedge_quickjs.wasm example_js/hello.js

Next, we will discuss more advanced use cases for JavaScript in WasmEdge.