Firebase functions cannot deploy : SyntaxError: Unexpected token function - node.js

Question

I am trying to deploy a function to firebase and I get an error during deployment
Error: Functions did not deploy properly.
Could it be linked with the async function ?
Actual behavior
Functions get deployed with errors, the cli shows me the following message:
================ console log ================
> eslint .
✔ functions: Finished running predeploy script.
i functions: ensuring necessary APIs are enabled...
✔ functions: all necessary APIs are enabled
i functions: preparing functions directory for uploading...
i functions: packaged functions (56.39 KB) for uploading
✔ functions: functions folder uploaded successfully
i functions: updating function sendContactEmailOAuth...
⚠ functions[sendContactEmailOAuth]: Deployment error.
Function load error: Code in file index.js can't be loaded.
Is there a syntax error in your code?
Detailed stack trace: /user_code/index.js:13
async function getJwt() {
^^^^^^^^
================ functions index.js file ================
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();
const { JWT } = require('google-auth-library/build/src/index');
exports.sendContactEmailOAuth = functions.https.onRequest((req, res) => {
const sender_msg = 'just a test'
const email = 'contact#lechorodescharentes.org'
async function getJwt() {
const client = new JWT(
functions.config().service_key.client_email,
null,
functions.config().service_key.private_key,
['https://www.googleapis.com/auth/cloud-platform', 'https://mail.google.com'],
);
await client.authorize();
const url = `https://www.googleapis.com/dns/v1/projects/${functions.config().service_key.project_id}`;
const res = await client.request({ url });
console.log(res.data);
}
getJwt();
/* send email with nodemailer to be inserted here */
});
================ package.json file ================
{
"name": "functions",
"description": "Cloud Functions for Firebase",
"scripts": {
"lint": "eslint .",
"serve": "firebase serve --only functions",
"shell": "firebase functions:shell",
"start": "npm run shell",
"deploy": "firebase deploy --only functions",
"logs": "firebase functions:log"
},
"dependencies": {
"firebase-admin": "~5.12.0",
"firebase-functions": "^1.0.2",
"firebase-tools": "^3.18.4",
"google-auth-library": "^1.4.0",
"nodemailer": "^4.6.4"
},
"devDependencies": {
"eslint": "^4.12.0",
"eslint-plugin-promise": "^3.6.0"
},
"private": true
}

Answer 1

As of September 2019:
Update firebase-admin : npm install --save firebase-admin
Update firebase-functions : npm install --save firebase-functions
Add "engines": { "node": "10" } to your /functions/package.json
...
"dependencies": {
"firebase-admin": "^8.5.0",
"firebase-functions": "^3.2.0"
},
"devDependencies": {
"tslint": "~5.19.0",
"typescript": "~3.6.2"
},
"engines": {
"node": "10"
}
...
As of August 2018:
Cloud Functions now support Node 8 (8.11.1). Check out this blog post.
Upgrade to Node 8
As suggested in this blog post, follow these steps to upgrade to Node 8:
Upgrade your firebase-functions version via npm install --save firebase-functions#latest
Upgrade firebase-tools via npm update -g firebase-tools
Add "engines": { "node": "8" } to your /functions/package.json

Answer 2

If you are still having the issue on a recent version (such as node 12), use the ecmaVersion parser option in your .eslintrc.js file.
Here's a sample:
module.exports = {
root: true,
env: {
es6: true,
node: true,
},
parserOptions: {
ecmaVersion: 8,
},
extends: [
"eslint:recommended",
"google",
],
rules: {
quotes: ["error", "double"],
},
};
h/t to Dean for the original suggestion.