chrome.runtime.onMessage response with async await

Question

I want to use async await in an onMessage listener:

chrome.runtime.onMessage.addListener(async (request, sender, sendResponse) =>{
    var key = await getKey(         


        

Answer 1

Not sure if Chrome extension runtime environment supports the async/await syntax, but you can use a transpiler (i.e. Babel) to have it converted to for example ES5. Then you can define a wrapper function like this:

function asChromeListener(listener) {
  return (message, sender, sendResponse) => {
    const returnValue = listener(message, sender);

    if (isPromise(returnValue)) {
      returnValue.then(sendResponse);
      return true;
    }
    else {
      if (typeof returnValue !== 'undefined') {
        sendResponse(returnValue);
      }
      return false;
    }
  };
}

function isPromise(value) {
  return typeof value === 'object' && value !== null && 'then' in value && 'catch' in value;
}

Which you can then use like:

chrome.runtime.onMessage.addListener(asChromeListener(async (message, sender) => {
  return await doMyAsyncWork(message);
});

Since we use TypeScript, here's also the snippet that we actually use (with generic types).

export function asChromeListener(listener: (message: M, sender: S) => any) {
  return (message: M, sender: S, sendResponse: R) => {
    const returnValue = listener(message, sender);

    if (isPromise(returnValue)) {
      returnValue.then(sendResponse);
      return true;
    }
    else {
      if (typeof returnValue !== 'undefined') {
        sendResponse(returnValue);
      }
      return false;
    }
  };
}

function isPromise(value: any) {
  return typeof value === 'object' && value !== null && 'then' in value && 'catch' in value;
}