Yeah, you can follow this example in Github: https://github.com/VapiAI/client-sdk-html-script-tag. After Vapi initialiazation:

window.vapiSDK.vapi = vapi;

you can call

const call = await window.vapiSDK.vapi.start(assistantId);

to start the conversation and

window.vapiSDK.vapi.stop();

to stop it.