Category: JavaScript

To create a Express.js middleware that accepts parameters with JavaScript, we return a function that takes the arguments we want.

For instance, we write

const hasRole = (role) => {
  return (req, res, next) => {
    if (role !== req.user.role) {
      res.redirect("...");
    } else {
      next();
    }
  };
};

const middlwareHasRoleAdmin = hasRole("admin");

app.get("/hasToBeAdmin", middlwareHasRoleAdmin, (req, res) => {});

to define the hasRole function.

It returns a middleware function that checks the role and either redirects with res.redirect or move to the next middleware with next.

Then we call hasRole with 'admin' to return a middleware with role set to 'admin'.

And we use the middlwareHasRoleAdmin middleware in our /hasToBeAdmin route.

To install only "devDependencies" using npm, we use the --only-dev option.

To use it, we run

npm install --only=dev

to use the --only-dev option to only install dev dependencies.

To install Node.js as windows service, we use the node-windows package.

For instance, we write

const Service = require("node-windows").Service;

const svc = new Service({
  name: "Hello World",
  description: "The nodejs.org example web server.",
  script: "C:\\path\\to\\helloworld.js",
});

svc.on("install", () => {
  svc.start();
});

svc.install();

to create a Service object with the name, description and the program location.

Then we listen for the install event with on and call start to start the service once it’s installed.

Finally, we call install to install the service.

To include JavaScript class definition from another file in Node.js, we set the class as the value of module.exports.

For instance, in user.js, we write

class User {
  //...
}

module.exports = User;

to export the User class.

Then in app.js, we write

const User = require("./user.js");

let user = new User();

to import the user.js file with required.

And then we create a User object.

To fix Mongoose’s find method with $or condition does not work properly with JavaScript, we set $or to an array with the conditions we’re searching for.

For instance, we write

const ObjectId = require("mongoose").Types.ObjectId;
const objId = new ObjectId(param.length < 12 ? "123456789012" : param);

User.find(
  { $or: [{ _id: objId }, { name: param }, { nickname: param }] },
  (err, docs) => {
    if (!err) res.send(docs);
  }
);

to call find with an object with $or set to an object with the conditions we’re looking for.

We get the results from the docs parameter in the callback.