Author: John Au-Yeung

To fix the ‘Failed to connect to 127.0.0.1:27017, reason: errno:111 Connection refused’ error with Node MongoDB, we remove the Mongo lock file.

To do this, we run

sudo rm /var/lib/mongodb/mongod.lock
sudo service mongod restart

to remove the mongod.lock file with rm.

Then we restart the Mongo server with service mongod restart.

To wait until an element is visible with JavaScript Puppeteer, we call waitForSelector.

For instance, we write

const puppeteer = require("puppeteer");

const broswer = await puppeteer.launch();
const page = await browser.newPage();
await page.waitForSelector("#myId");
browser.close();

to call launch to launch the browser.

We call awaitForSelector to wait for the element with ID myId to show.

To destroy cookie with Node.js, we call clearCookie.

For instance, we write

res.clearCookie("key");

to call clearCookie to clear the cookie with key 'key'.

To combine or merge JSON on Node.js, we use the spread operator.

For instance, we write

const o1 = { a: 1 };
const o2 = { b: 2 };
const obj = { ...o1, ...o2 };

to create the obj object by spreading the properties of o1 and o2 into a new object.

To export an async function in Node.js, we set the module.exports property.

For instance, we write

const doStuff = async () => {
  // ...
};

module.exports.doStuff = doStuff;

to define the doStuff function and set that as the value of the module.exports.doStuff to export it.