How to use console in node.js
In this article, we'll learn how to use most methods available in the nodeJS console class more effectively.
In this article, we'll learn how to use most methods available in the nodeJS console class more effectively.
IntroductionTable of Contents
- Introduction
- console.log, console.info and console.debug
- console.table
- Arrays
- Objects
- console.dir
- console.dirxml
- console.assert
- console.error & console.warn
- console.trace(label)
- console.count(label)
- console.countReset(label)
- console.time(label) and console.timeEnd(label)
- Conclusion
- Feedback
To demonstrate, I’ll use Chrome browser version 70.0.3538.77 and nodeJS version 8.11.** 3**.
Okay then. Let’s begin.
console.log, console.info and console.debugconsole.log(string, substitution)
While the famed console.log method really needs no introduction, you’ll be glad to know that the console.info and console.debug methods are identical to console.log in their operation.
You can use console.debug in the Firefox browser console by default but to use it in Chrome, you’ll have to set the log level to verbose like this.
The console.log method prints to standard out, whether this be the terminal or browser console. It outputs strings by default but can be used in conjuction with template strings to modify what it returns.
Here’s how it works:
The arguments in the template string are passed to util.format which then processes the arguments by replacing each substitution token with the respective converted value. The supported substitution tokens are:
%s
const msg = `Using the console class`;
console.log('%s', msg); // Using the console class
console.log(msg); // Using the console class
%s is the default substitution pattern.
%d, %f, %i, %o
const circle = (radius = 1) => {
const profile = {};
const pi = 22/7;
profile.diameter = 2_pi_radius;
profile.circumference = pi_radius_2;
profile.area = pi_radius^2;
profile.volume = 4/3_pi_radius^3;
console.log('This circle has a radius of: %d cm', radius);
console.log('This circle has a circumference of: %f cm', profile.diameter);
console.log('This circle has an area of: %i cm^2', profile.area);
console.log('The profile of this cirlce is: %o', profile);
console.log('Diameter %d, Area: %f, Circumference %i', profile.diameter, profile.area, profile.circumference)
}
circle();
This is what happens:
%d will be substituted by a digit (integer or float). %f will be replaced by a float value. %i will be replaced by an integer. %o will be replaced by an Object.
%o is especially handy because we don’t have to use JSON.stringify to expand our object because it shows all the object’s properties by default.
Note that you can use as many token substitutions as you like. They’ll just be replaced the same order as the arguments you pass.
%c
This substitution token applies css styles to the subsituted text.
console.log('LOG LEVEL: %c OK', 'color: green; font-weight: normal');
console.log('LOG LEVEL: %c PRIORITY', 'color: blue; font-weight: medium');
console.log('LOG LEVEL: %c WARN', 'color: red; font-weight: bold');
console.log('ERROR HERE');
Here it is in action.
Above, we note that the text we pass to console.log after the %c substitution token is affected by the styles, but the text before is left as is without styling.
console.tableThe first argument passed to it is the data to be returned in the form of a table. The second is an array of selected columns to be displayed.
console.table(tabularData, [properties])
This method will print the input passed to it formatted as a table then log the input object after the table representation.
Arrays
If an array is passed to it as data, each element in the array will be a row in the table.
const books = ['The Silmarillion', 'The Hobbit', 'Unfinished Tales'];
console.table(books);
With a simple array with a depth of 1, the first column in the table has the heading index. Under the index header in the first column are the array indexes and the items in the array are listed in the second column under the value header.
This is what happens for a nested array.
const authorsAndBooks = [['Tolkien', 'Lord of The Rings'],['Rutger', 'Utopia For Realists'], ['Sinek', 'Leaders Eat Last'], ['Eyal', 'Habit']];
console.table(authorsAndBooks);
Objects
For objects with a depth of 1, the object keys will be listed under the index header and the values in the object under the second column header.
const inventory = { apples: 200, mangoes: 50, avocados: 300, kiwis: 50 };
console.table(inventory);
For nested objects,
const forexConverter = { asia: { rupee: 1.39, renminbi: 14.59 , ringgit: 24.26 }, africa: { rand: 6.49, nakfa: 6.7 , kwanza:0.33 }, europe: { swissfranc: 101.60, gbp: 130, euro: 115.73 } };
console.table(forexConverter);
Some more nested objects,
const workoutLog = { Monday: { push: 'Incline Bench Press', pull: 'Deadlift'}, Wednesday: { push: 'Weighted Dips', pull: 'Barbell Rows'}};
console.table(workoutLog);
Here, we specify that we only want to see data under the column push.
console.table(workoutLog, 'push');
To sort the data under a column, just click the column header.
Pretty handy, eh?
Try passing console.table an object with some values as arrays!## console.dir
The first argument passed to this function is the object to be logged while the second is an object containing options that will define how the resulting output is fomatted or what properties in the object will be shown.
What’s returned is an object formatted by node’s util.inspect function.
Nested or child objects within the input object are expandable under disclosure triangles.
console.dir(object, options);
// where options = { showHidden: true ... }
Let’s see this in action.
const user = {
details: {
name: {
firstName: 'Immanuel',
lastName: 'Kant'
},
height: `1.83m"`,
weight: '90kg',
age: '80',
occupation: 'Philosopher',
nationality: 'German',
books: [
{
name: 'Critique of Pure Reason',
pub: '1781',
},
{
name: 'Critique of Judgement',
pub: '1790',
},
{
name: 'Critique of Practical Reason',
pub: '1788',
},
{
name: 'Perpetual Peace',
pub: '1795',
},
],
death: '1804'
}
}
console.dir(user);
Here it is in the Chrome console.
console.dirxmlThis function will render an interactive tree of the XML/HTML it is passed. It defaults to a Javascript object if it’s not possible to render the node tree.
console.dirxml(object|nodeList);
Much like console.*_dir, *_the rendered tree can be expanded through clicking disclosure triangles within which you can see child nodes.
It’s output is similar to that which we find under the Elements tab in the browser.
This is how it looks when we pass in some HTML from a Wikipedia page.
Let’s pass in some HTML from a page on this website.
This is how it looks when we pass in an object.
Try passing console.table an object with some values as arrays!## console.assert
The first argument passed to the function is a value to test as truthy. All other arguments passed are considered messages to be printed out if the value passed is not evaluated as truthy.
The Node REPL will throw an error halting execution of subsequent code.
console.assert(value, [...messages])
Here’s a basic example:
console.assert(false, 'Assertion failed'); // Assertion failed
Now, let’s have some fun. We’ll build a mini testing framework using console.assert
const sum = (a = 0, b = 0) => Number(a) + Number(b);
function test(functionName, actualFunctionResult, expected) {
const actual = actualFunctionResult;
const pass = actual === expected;
console.assert(pass, `Assertion failed for ${functionName}`);
return `Test passed ${actual} === ${expected}`;
}
console.log(test('sum', sum(1,1), 2)); // Test passed 2 === 2
console.log(test('sum', sum(), 0)); // Test passed 0 === 0
console.log(test('sum', sum, 2)); // Assertion failed for sum
console.log(test('sum', sum(3,3), 4)); // Assertion failed for sum
Run the above in your node REPL or browser console to see what happens.
console.error & console.warnThese two are essentially identical. They will both print whatever string is passed to them.
However, console.warn prints out a triangle warn symbol before the message passed while console.error prints out a danger symbol before the message passed.
console.error(string, substitution);
console.warn(string, substitution);
Let’s note that string substitution can be applied in the same way as the console.log method.
Here’s a mini logging function using console.error.
const sum = (a = 0, b = 0) => Number(a) + Number(b);
function otherTest(actualFunctionResult, expected) {
if (actualFunctionResult !== expected) {
console.error(new Error(`Test failed ${actualFunctionResult} !== ${expected}`));
} else {
// pass
}
}
otherTest(sum(1,1), 3);
This console method will prints the string Trace: followed by the label passed to the function then the stack trace to the current position of the function.
function getCapital(country) {
const capitalMap = {
belarus: 'minsk', australia: 'canberra', egypt: 'cairo', georgia: 'tblisi', latvia: 'riga', samoa: 'apia'
};
console.trace('Start trace here');
return Object.keys(capitalMap).find(item => item === country) ? capitalMap[country] : undefined;
}
console.log(getCapital('belarus'));
console.log(getCapital('accra'));
Count will begin and increment a counter of name label** .**
Let’s build a word counter to see how it works.
const getOccurences = (word = 'foolish') => {
const phrase = `Oh me! Oh life! of the questions of these recurring, Of the endless trains of the faithless, of cities fill’d with the foolish, Of myself forever reproaching myself, for who more foolish than I, and who more faithless?`;
let count = 0;
const wordsFromPhraseArray = phrase.replace(/[,.!?]/igm, '').split(' ');
wordsFromPhraseArray.forEach((element, idx) => {
if (element === word) {
count ++;
console.count(word);
}
});
return count;
}
getOccurences();
Here, we see that the word foolish was logged twice. Once for each appearance of the word in the phrase.
We could use this as a handy method to see how many times a function was called or how many times a line in our code executed.
console.countReset(label)As the name suggests, this resets a counter having a label set by the console.count method.
const getOccurences = (word = 'foolish') => {
const phrase = `Oh me! Oh life! of the questions of these recurring, Of the endless trains of the faithless, of cities fill’d with the foolish, Of myself forever reproaching myself, for who more foolish than I, and who more faithless?`;
let count = 0;
const wordsFromPhraseArray = phrase.replace(/[,.!?]/igm, '').split(' ');
wordsFromPhraseArray.forEach((element, idx) => {
if (element === word) {
count ++;
console.count(word);
console.countReset(word);
}
});
return count;
}
getOccurences();
We can see that our getOccurences function returns 2 because there are indeed two occurences of the word foolish in the phrase but since our counter is reset at every match, it logs foolish: 1twice.
console.time(label) and console.timeEnd(label)The console.time function starts a timer with the label supplied as an argument to the function, while the console.*_timeEnd *_function stops a timer with the **label supplied as an argument to the function.
console.time('<timer-label>');
console.timeEnd('<timer-label'>);
We can use it to figure out how much time it took to run an operation by passing in the same label name to both functions.
const users = ['Vivaldi', 'Beethoven', 'Ludovico'];
const loop = (array) => {
array.forEach((element, idx) => {
console.log(element);
})
}
const timer = () => {
console.time('timerLabel');
loop(users);
console.timeEnd('timerLabel');
}
timer();
We can see the timer label displayed against time value after the timer is stopped.
It took the loop function 0.6909ms to finish looping through the array.
ConclusionAt last, we’ve come to the end of this tutorial. I hope you’ve enjoyed it.
I’ve left out the non standard uses of the console class like console.profile, console.profileEnd and console.timeLog , but feel free to experiment with them and let me know how it goes.
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How to Use Express.js, Node.js and MongoDB.js
In this post, I will show you how to use Express.js, Node.js and MongoDB.js. We will be creating a very simple Node application, that will allow users to input data that they want to store in a MongoDB database. It will also show all items that have been entered into the database.
In this post, I will show you how to use Express.js, Node.js and MongoDB.js. We will be creating a very simple Node application, that will allow users to input data that they want to store in a MongoDB database. It will also show all items that have been entered into the database.
Creating a Node ApplicationTo get started I would recommend creating a new database that will contain our application. For this demo I am creating a directory called node-demo. After creating the directory you will need to change into that directory.
mkdir node-demo
cd node-demo
Once we are in the directory we will need to create an application and we can do this by running the command
npm init
This will ask you a series of questions. Here are the answers I gave to the prompts.
The first step is to create a file that will contain our code for our Node.js server.
touch app.js
In our app.js we are going to add the following code to build a very simple Node.js Application.
var express = require("express");
var app = express();
var port = 3000;
app.get("/", (req, res) => {
res.send("Hello World");
});
app.listen(port, () => {
console.log("Server listening on port " + port);
});
What the code does is require the express.js application. It then creates app by calling express. We define our port to be 3000.
The app.use line will listen to requests from the browser and will return the text “Hello World” back to the browser.
The last line actually starts the server and tells it to listen on port 3000.
Installing ExpressOur app.js required the Express.js module. We need to install express in order for this to work properly. Go to your terminal and enter this command.
npm install express --save
This command will install the express module into our package.json. The module is installed as a dependency in our package.json as shown below.
To test our application you can go to the terminal and enter the command
node app.js
Open up a browser and navigate to the url http://localhost:3000
You will see the following in your browser
Creating Website to Save Data to MongoDB DatabaseInstead of showing the text “Hello World” when people view your application, what we want to do is to show a place for user to save data to the database.
We are going to allow users to enter a first name and a last name that we will be saving in the database.
To do this we will need to create a basic HTML file. In your terminal enter the following command to create an index.html file.
touch index.html
In our index.html file we will be creating an input filed where users can input data that they want to have stored in the database. We will also need a button for users to click on that will add the data to the database.
Here is what our index.html file looks like.
<!DOCTYPE html>
<html>
<head>
<title>Intro to Node and MongoDB<title>
<head>
<body>
<h1>Into to Node and MongoDB</h1>
<form method="post" action="/addname">
<label>Enter Your Name</label><br>
<input type="text" name="firstName" placeholder="Enter first name..." required>
<input type="text" name="lastName" placeholder="Enter last name..." required>
<input type="submit" value="Add Name">
</form>
<body>
<html>
If you are familiar with HTML, you will not find anything unusual in our code for our index.html file. We are creating a form where users can input their first name and last name and then click an “Add Name” button.
The form will do a post call to the /addname endpoint. We will be talking about endpoints and post later in this tutorial.
Displaying our Website to UsersWe were previously displaying the text “Hello World” to users when they visited our website. Now we want to display our html file that we created. To do this we will need to change the app.use line our our app.js file.
We will be using the sendFile command to show the index.html file. We will need to tell the server exactly where to find the index.html file. We can do that by using a node global call __dirname. The __dirname will provide the current directly where the command was run. We will then append the path to our index.html file.
The app.use lines will need to be changed to
app.use("/", (req, res) => { res.sendFile(__dirname + "/index.html"); });
Once you have saved your app.js file, we can test it by going to terminal and running node app.js
Open your browser and navigate to “http://localhost:3000”. You will see the following
Connecting to the DatabaseNow we need to add our database to the application. We will be connecting to a MongoDB database. I am assuming that you already have MongoDB installed and running on your computer.
To connect to the MongoDB database we are going to use a module called Mongoose. We will need to install mongoose module just like we did with express. Go to your terminal and enter the following command.
npm install mongoose --save
This will install the mongoose model and add it as a dependency in our package.json.
Connecting to the DatabaseNow that we have the mongoose module installed, we need to connect to the database in our app.js file. MongoDB, by default, runs on port 27017. You connect to the database by telling it the location of the database and the name of the database.
In our app.js file after the line for the port and before the app.use line, enter the following two lines to get access to mongoose and to connect to the database. For the database, I am going to use “node-demo”.
var mongoose = require("mongoose"); mongoose.Promise = global.Promise; mongoose.connect("mongodb://localhost:27017/node-demo");
Once the user enters data in the input field and clicks the add button, we want the contents of the input field to be stored in the database. In order to know the format of the data in the database, we need to have a Schema.
For this tutorial, we will need a very simple Schema that has only two fields. I am going to call the field firstName and lastName. The data stored in both fields will be a String.
After connecting to the database in our app.js we need to define our Schema. Here are the lines you need to add to the app.js.
var nameSchema = new mongoose.Schema({ firstName: String, lastNameName: String });
Once we have built our Schema, we need to create a model from it. I am going to call my model “DataInput”. Here is the line you will add next to create our mode.
var User = mongoose.model("User", nameSchema);
Now that we have a connection to our database, we need to create the mechanism by which data will be added to the database. This is done through our REST API. We will need to create an endpoint that will be used to send data to our server. Once the server receives this data then it will store the data in the database.
An endpoint is a route that our server will be listening to to get data from the browser. We already have one route that we have created already in the application and that is the route that is listening at the endpoint “/” which is the homepage of our application.
HTTP Verbs in a REST APIThe communication between the client(the browser) and the server is done through an HTTP verb. The most common HTTP verbs are
GET, PUT, POST, and DELETE.
The following table explains what each HTTP verb does.
| HTTP Verb | Operation |
|---|---|
| GET | Read |
| POST | Create |
| PUT | Update |
| DELETE | Delete |
As you can see from these verbs, they form the basis of CRUD operations that I talked about previously.
Building a CRUD endpointIf you remember, the form in our index.html file used a post method to call this endpoint. We will now create this endpoint.
In our previous endpoint we used a “GET” http verb to display the index.html file. We are going to do something very similar but instead of using “GET”, we are going to use “POST”. To get started this is what the framework of our endpoint will look like.
app.post("/addname", (req, res) => {
});
To fill out the contents of our endpoint, we want to store the firstName and lastName entered by the user into the database. The values for firstName and lastName are in the body of the request that we send to the server. We want to capture that data, convert it to JSON and store it into the database.
Express.js version 4 removed all middleware. To parse the data in the body we will need to add middleware into our application to provide this functionality. We will be using the body-parser module. We need to install it, so in your terminal window enter the following command.
npm install body-parser --save
Once it is installed, we will need to require this module and configure it. The configuration will allow us to pass the data for firstName and lastName in the body to the server. It can also convert that data into JSON format. This will be handy because we can take this formatted data and save it directly into our database.
To add the body-parser middleware to our application and configure it, we can add the following lines directly after the line that sets our port.
var bodyParser = require('body-parser');
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
Mongoose provides a save function that will take a JSON object and store it in the database. Our body-parser middleware, will convert the user’s input into the JSON format for us.
To save the data into the database, we need to create a new instance of our model that we created early. We will pass into this instance the user’s input. Once we have it then we just need to enter the command “save”.
Mongoose will return a promise on a save to the database. A promise is what is returned when the save to the database completes. This save will either finish successfully or it will fail. A promise provides two methods that will handle both of these scenarios.
If this save to the database was successful it will return to the .then segment of the promise. In this case we want to send text back the user to let them know the data was saved to the database.
If it fails it will return to the .catch segment of the promise. In this case, we want to send text back to the user telling them the data was not saved to the database. It is best practice to also change the statusCode that is returned from the default 200 to a 400. A 400 statusCode signifies that the operation failed.
Now putting all of this together here is what our final endpoint will look like.
app.post("/addname", (req, res) => {
var myData = new User(req.body);
myData.save()
.then(item => {
res.send("item saved to database");
})
.catch(err => {
res.status(400).send("unable to save to database");
});
});
Save your code. Go to your terminal and enter the command node app.js to start our server. Open up your browser and navigate to the URL “http://localhost:3000”. You will see our index.html file displayed to you.
Make sure you have mongo running.
Enter your first name and last name in the input fields and then click the “Add Name” button. You should get back text that says the name has been saved to the database like below.
Access to CodeThe final version of the code is available in my Github repo. To access the code click here. Thank you for reading !
Node.js for Beginners - Learn Node.js from Scratch (Step by Step)
Node.js for Beginners - Learn Node.js from Scratch (Step by Step) - Learn the basics of Node.js. This Node.js tutorial will guide you step by step so that you will learn basics and theory of every part. Learn to use Node.js like a professional. You’ll learn: Basic Of Node, Modules, NPM In Node, Event, Email, Uploading File, Advance Of Node.
Node.js for BeginnersLearn Node.js from Scratch (Step by Step)
Welcome to my course "Node.js for Beginners - Learn Node.js from Scratch". This course will guide you step by step so that you will learn basics and theory of every part. This course contain hands on example so that you can understand coding in Node.js better. If you have no previous knowledge or experience in Node.js, you will like that the course begins with Node.js basics. otherwise if you have few experience in programming in Node.js, this course can help you learn some new information . This course contain hands on practical examples without neglecting theory and basics. Learn to use Node.js like a professional. This comprehensive course will allow to work on the real world as an expert!
What you’ll learn:
- Basic Of Node
- Modules
- NPM In Node
- Event
- Uploading File
- Advance Of Node
Top 7 Most Popular Node.js Frameworks You Should Know
Node.js is an open-source, cross-platform, runtime environment that allows developers to run JavaScript outside of a browser. In this post, you'll see top 7 of the most popular Node frameworks at this point in time (ranked from high to low by GitHub stars).
Node.js is an open-source, cross-platform, runtime environment that allows developers to run JavaScript outside of a browser.
One of the main advantages of Node is that it enables developers to use JavaScript on both the front-end and the back-end of an application. This not only makes the source code of any app cleaner and more consistent, but it significantly speeds up app development too, as developers only need to use one language.
Node is fast, scalable, and easy to get started with. Its default package manager is npm, which means it also sports the largest ecosystem of open-source libraries. Node is used by companies such as NASA, Uber, Netflix, and Walmart.
But Node doesn't come alone. It comes with a plethora of frameworks. A Node framework can be pictured as the external scaffolding that you can build your app in. These frameworks are built on top of Node and extend the technology's functionality, mostly by making apps easier to prototype and develop, while also making them faster and more scalable.
Below are 7of the most popular Node frameworks at this point in time (ranked from high to low by GitHub stars).
ExpressWith over 43,000 GitHub stars, Express is the most popular Node framework. It brands itself as a fast, unopinionated, and minimalist framework. Express acts as middleware: it helps set up and configure routes to send and receive requests between the front-end and the database of an app.
Express provides lightweight, powerful tools for HTTP servers. It's a great framework for single-page apps, websites, hybrids, or public HTTP APIs. It supports over fourteen different template engines, so developers aren't forced into any specific ORM.
MeteorMeteor is a full-stack JavaScript platform. It allows developers to build real-time web apps, i.e. apps where code changes are pushed to all browsers and devices in real-time. Additionally, servers send data over the wire, instead of HTML. The client renders the data.
The project has over 41,000 GitHub stars and is built to power large projects. Meteor is used by companies such as Mazda, Honeywell, Qualcomm, and IKEA. It has excellent documentation and a strong community behind it.
KoaKoa is built by the same team that built Express. It uses ES6 methods that allow developers to work without callbacks. Developers also have more control over error-handling. Koa has no middleware within its core, which means that developers have more control over configuration, but which means that traditional Node middleware (e.g. req, res, next) won't work with Koa.
Koa already has over 26,000 GitHub stars. The Express developers built Koa because they wanted a lighter framework that was more expressive and more robust than Express. You can find out more about the differences between Koa and Express here.
SailsSails is a real-time, MVC framework for Node that's built on Express. It supports auto-generated REST APIs and comes with an easy WebSocket integration.
The project has over 20,000 stars on GitHub and is compatible with almost all databases (MySQL, MongoDB, PostgreSQL, Redis). It's also compatible with most front-end technologies (Angular, iOS, Android, React, and even Windows Phone).
NestNest has over 15,000 GitHub stars. It uses progressive JavaScript and is built with TypeScript, which means it comes with strong typing. It combines elements of object-oriented programming, functional programming, and functional reactive programming.
Nest is packaged in such a way it serves as a complete development kit for writing enterprise-level apps. The framework uses Express, but is compatible with a wide range of other libraries.
LoopBackLoopBack is a framework that allows developers to quickly create REST APIs. It has an easy-to-use CLI wizard and allows developers to create models either on their schema or dynamically. It also has a built-in API explorer.
LoopBack has over 12,000 GitHub stars and is used by companies such as GoDaddy, Symantec, and the Bank of America. It's compatible with many REST services and a wide variety of databases (MongoDB, Oracle, MySQL, PostgreSQL).
HapiSimilar to Express, hapi serves data by intermediating between server-side and client-side. As such, it's can serve as a substitute for Express. Hapi allows developers to focus on writing reusable app logic in a modular and prescriptive fashion.
The project has over 11,000 GitHub stars. It has built-in support for input validation, caching, authentication, and more. Hapi was originally developed to handle all of Walmart's mobile traffic during Black Friday.