Node.js Tips

Node.js Tips — Promises,, and Passing Data in Express

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Like any kind of apps, there are difficult issues to solve when we write Node apps.

In this article, we’ll look at some solutions to common problems when writing Node apps.

Share Constants in NodeJS Modules

We can share constants in Node modules by exporting a frozen object.

For instance, we can write:


module.exports = Object.freeze({
  FOO: 'foo',
  BAR: '123'

We call the Object.freeze method to freeze the object with the constants.

Then in another module, we can require by writing:

const constants = require('./constants');

Send Responses to All Clients Except Sender with

There are multiple ways to send a response to all clients except the sender with

Yo send to the sender only, we can write:

socket.emit('message', "hello");

To send to all clients except the sender, we can write:

socket.broadcast.emit('message', "hello");

To send to all clients in a room except for the sender, we can write:'chatRoom').emit('message', 'hello');

To send to all clients including the sender, we write:

io.emit('message', "hello");

To send to all clients in a room including the sender, we can write:'chatRoom').emit('message', 'hello');

To send to the sender only in a room, we can write:

`'`chatRoom`').emit('message', 'hello');`

To send to all clients in a namespace, we can write:

io.of('namespace').emit('message', 'hello');

To send to a socket ID, we can write:'message', 'hello');

Reasons to use Promise Libraries like Q or BlueBird

We can use promise libraries like Q or Bluebird to convert existing async functions to return promises.

For instance, we can write:

const Promise = require('bluebird');
const fs = Promise.promisifyAll(require('fs'));

fs.readFileAsync('foo.text').then((data) => {

We used Bluebird to convert everything in the fs module to promises.

So we can use methods like readFileAsync to read files asynchronously.

There are also methods exclusive to Bluebird that aren’t available with the ES6 Promise constructor.

Promise.promisify() converts Node callbacks to promises. maps arrays to promises.

Promise.reduce() lets us map values to promises and invoke them sequentially and reduce the resolved values to a single value.

Promise.mapSeries() takes values, map them to promises, and run them in series.

Then we get the values of them at the end.

Promise.delay() lets us dealt a promise by a given number of milliseconds.

Node.js Global Variables

We can add a property to global to add a global variable.

For instance, we can write:

global._ = `require('underscore');`

Node.js Get File Extension

We can get the file extension of a file name with the extname method.

For instance, we can write:

const path = require('path');


Run Function in Script from Command Line

We can run a function in a script from the command line with node -e .

If we have a module, we can write:


module.exports.hello = () => {

For instance, we can write:

node -e 'require("./hi").hello()'

Difference Between res.send and res.json in Express.js

res.send and res.json are the same when arrays or objects are passed in.

However, if non-objects are passed in, then res.json also converts those values to something that can be returned.

res.json calls res.send in the end.

Passing Variables to the Next Middleware Using next() in Express.js

We add a property to the req variable to pass data to the next middleware.

For instance, we can write: = 'bar';

Then we can access in the next middleware.

Also, we can add a property to the res.locals property to do the same thing.

Use Node.js Crypto to Create an HMAC-SHA1 Hash

We can use the Node crypto module to create an HMAC-SHA1 hash.

For instance, we can write:

const crypto = require('crypto')

const text = 'hello world';
const key = 'secret';

crypto.createHmac('sha1', key)

We call the createHmac method to create a hash from the key .

And then we hash the text with it with update and convert it to hex with update .


We can use the crypto module to hash text.

There are many ways to send data with

We can get the extension of a file name with the path module.

Promise libraries are still useful.

global is the global object in Node.

By John Au-Yeung

Web developer specializing in React, Vue, and front end development.

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