Node.js Console Log Examples

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Ah, the humble console.log(). It's the first thing most of us encounter when we dive into the world of JavaScript. Whether you're trying to debug an issue, display some information, or just want to check if your code is even running, console.log() has got your back. In this article, we’ll explore various ways to use console.log() in a Node.js environment and make your debugging life a whole lot easier.

Basic Usage of console.log()

Starting off with the basics, the simplest form of console.log() is to directly print strings or numbers to the console.

console.log("Hello, Node.js!");
console.log(42);

Running this code in a Node.js environment will produce the following output:

Hello, Node.js!
42

Concatenating Strings and Variables

Just like in the browser, you can concatenate strings and variables. This is useful when you want to display dynamic content.

let userName = "Alice";
console.log("Welcome, " + userName + "!");

Output:

Welcome, Alice!

Notice how we used the + operator to combine the string "Welcome, " with the value of userName and the string "!".

Using Template Literals

If you want a cleaner way to include variables in your strings, JavaScript's template literals are your friend. This makes the code more readable and avoids the messy concatenation.

let userName = "Bob";
console.log(`Welcome, ${userName}!`);

Output:

Welcome, Bob!

Logging Objects and Arrays

In Node.js, you can also log objects and arrays.

let user = {
    name: "Charlie",
    age: 30
};

let hobbies = ["reading", "gaming", "coding"];

console.log(user);
console.log(hobbies);

Output:

{ name: 'Charlie', age: 30 }
[ 'reading', 'gaming', 'coding' ]

Formatting Output

For more advanced logging, console.log() supports formatting specifiers like %s for strings, %d for numbers, and %j for JSON.

let userName = "David";
let age = 25;

console.log("User: %s, Age: %d", userName, age);

Output:

User: David, Age: 25

Using console.dir()

While console.log() is great for most cases, sometimes you need to inspect objects more thoroughly. This is where console.dir() comes in handy.

let user = {
    name: "Eve",
    age: 28,
    hobbies: ["painting", "hiking"]
};

console.dir(user, { depth: null, colors: true });

Output (with colors if your terminal supports it):

{ name: 'Eve', age: 28, hobbies: [ 'painting', 'hiking' ] }

Logging with Different Levels

Node.js also supports different logging levels such as console.info(), console.warn(), and console.error() to categorize your log messages.

console.info("This is an informational message.");
console.warn("This is a warning message.");
console.error("This is an error message.");

Output:

This is an informational message.
This is a warning message.
This is an error message.

Timing with console.time() and console.timeEnd()

If you need to measure how long a piece of code takes to execute, you can use console.time() and console.timeEnd().

console.time("loop");

for (let i = 0; i < 1000000; i++) {
    // Some intensive task
}

console.timeEnd("loop");

Output:

loop: 5.123ms

Counting with console.count()

To count the number of times a particular line of code is executed, use console.count().

for (let i = 0; i < 5; i++) {
    console.count("Loop executed");
}

Output:

Loop executed: 1
Loop executed: 2
Loop executed: 3
Loop executed: 4
Loop executed: 5

Grouping Logs

You can group multiple logs together using console.group() and console.groupEnd().

console.group("User Details");

console.log("Name: Frank");
console.log("Age: 40");
console.log("Occupation: Engineer");

console.groupEnd();

Output:

User Details
    Name: Frank
    Age: 40
    Occupation: Engineer

Customizing Console Output with chalk

For even more control over your console output, you can use the chalk library to add colors and styles.

First, install the chalk package:

npm install chalk

Then, use it in your code:

const chalk = require("chalk");

console.log(chalk.blue("Hello, world!"));
console.log(chalk.red.bold("Error: Something went wrong!"));
console.log(chalk.green("Success: Everything is working!"));

Output:

Hello, world! (in blue)
Error: Something went wrong! (in bold red)
Success: Everything is working! (in green)

FAQ

console.time("test");
// some code
console.timeEnd("test");