Author: John Au-Yeung

To fix MongoNetworkError: failed to connect to server [localhost:27017] on first connect with Node MongoDB, we should make sure we’re connecting to a reachable Mongo server.

For instance, we write

await mongoose.connect("mongodb://localhost/testdb");

to call mongoose.connect to connect to the testdb database on localhost.

The error shouldn’t be thrown if it’s reachable.

To Add, Delete new Columns in Node Sequelize CLI, we create a migration file.

For instance, we run

$ sequelize migration:create --name name_of_your_migration

to create a migration.

Then we write

module.exports = {
  up: (queryInterface, Sequelize) => {
    return queryInterface.addColumn("Todo", "completed", Sequelize.BOOLEAN);
  },

  down: (queryInterface, Sequelize) => {
    return queryInterface.removeColumn("Todo", "completed");
  },
};

to call addColumn to add a column with the table name, column name, and data type.

We call removeColumn with the table name and column name to remove it.

Then we run

$ sequelize db:migrate

to call the up function in the migration file.

To get the width and height of an image in Node.js, we use the image-size package.

For instance, we write

const sizeOf = require("image-size");

sizeOf("images/funny-cats.png", (err, dimensions) => {
  console.log(dimensions.width, dimensions.height);
});

to call the sizeOf function to read the images/funny-cats.png image.

And we get the width and height from the dimensions parameter in the callback.

To fix Date.now().toISOString() throwing error "not a function" with JavaScript, we call toISOString on a date object.

For instance, we write

const now = new Date();
const isoString = now.toISOString();

to create a new Date object now.

Then we call now.toISOString to return the datetime string from the date.

To convert a directory structure in the filesystem to JSON with Node.js, we use the directory-tree package.

To install it, we run

npm i directory-tree

Then we use it by writing

const directoryTree = require("directory-tree");

const tree = directoryTree("/some/path");
const filteredTree = directoryTree("/some/path", [".jpg", ".png"]);

to call directoryTree to return an object of the directory structure with the /some/path folder as root.

We can also call it with a 2nd argument to filter the items by extension.