Wasmo Docs

Write your first plugin


A Wasmo Builder instance running. If not, you should read the Getting started section.

Create your first greeting plugin

  1. Navigate to Wasmo UI
  2. From the plugins menu at the top left, click the Plus button.
  3. Select Javascript language from the list
  4. In the field that just appeared, add a Name for your plugin
  5. Click and edit the index.js file
function greet() {
    const name = Host.inputString()
    Host.outputString(`Hello, ${name}`)

module.exports = {greet}

Click the hammer icon at the top right of the screen to start the build process.

During the process the logs and errors are displayed in the terminal view at the bottom.

Once completed, your plugin should appear in the Releases section in the left sidebar. You can click on the item in the list to automatically download the WASM file.

Testing your first plugin

Wasmo binaries are strongly linked to Extism and this is why we have to run your WASM with their executable. You can download the Extism CLI on the releases page or using go with the following command.

go install github.com/extism/cli/extism@latest

Once downloaded, you can run the command by passing the function to call, the parameter to apply and the WASM file to execute.

extism call <your-plugin-file>.wasm greet \
    --input "Benjamin" \

If the command succeeds, you will see: Hello, Benjamin.

Congratulations, you have just created your first plugin!