Author: John Au-Yeung

To fix Uncaught TypeError: Object.values is not a function JavaScript, we can use Object.keys instead.

For instance, we write

const vals = Object.keys(countries).map((key) => {
  return countries[key];
});

to get the keys from the countries object with Object.keys.

Then we call map with a callback to get the value from each key in countries and return the array of values.

To fix Mongoose: CastError: Cast to ObjectId failed for value "[object Object]" at path "_id" with Node.js, we make sure we’re casting a valid value to an object ID.

For instance, we write

const mongoose = require("mongoose");

console.log(mongoose.Types.ObjectId.isValid("53cb6b9b4f4ddef1ad47f943"));
console.log(mongoose.Types.ObjectId.isValid("whatever"));

to use the mongoose.Types.ObjectId.isValid to check if the value we’re trying to cast to an object ID is a valid value.

The first console log should log true since it’s a valid object ID value.

And the 2nd one logs false since it’s not a valid object ID value.

To parse Query String in Node.js, we use the querystring module.

For instance, we write

const http = require("http");
const queryString = require("querystring");

http
  .createServer((oRequest, oResponse) => {
    let oQueryParams;
    if (oRequest.url.indexOf("?") >= 0) {
      oQueryParams = queryString.parse(oRequest.url.replace(/^.*\?/, ""));
      console.log(oQueryParams);
    }

    oResponse.writeHead(200, { "Content-Type": "text/plain" });
    oResponse.end("Hello world.");
  })
  .listen(3000, "127.0.0.1");

to call queryString.parse to parse the request URL that we got from oRequest.url.

We get pack an object with the keys and values of the query string.

To go back 1 folder level with __dirname with Node.js, we use the path.join method.

For instance, we write

const path = require("path");
const configFile = path.join(__dirname, "../test/karma.conf.js");

to call path.join with __dirname and a string with the path one level above __dirname with ../ to return a path one level above __dirname.

To pass execution arguments to app using Node.js PM2, we use the --

For instance, we run

pm2 start app.js -- --prod --second-arg --third-arg

to start app.js with start.

And then we pass in the arguments after --.