JavaScript console log() Method

In this chapter, we will learn about the console.log() method in JavaScript. This method is one of the most commonly used tools for debugging and displaying information in the browser’s console. We will cover:

• What is console.log()?
• Basic Usage
• Formatting Output
• Logging Multiple Values
• Logging Objects and Arrays
• Console Methods
• Simple Programs using console.log()

What is console.log()?

The console.log() method outputs a message to the web console. It is often used for testing purposes to check the values of variables and the flow of code.

Basic Usage

The console.log() method takes one or more parameters, which can be of any type, and prints them to the console.

Syntax

console.log(message);

Example

console.log("Hello, World!");

Output:

Hello, World!

Formatting Output

You can format the output of console.log() using format specifiers, similar to printf in C.

Example

let name = "Amit";
let age = 25;
console.log("Name: %s, Age: %d", name, age);

Output:

Name: Amit, Age: 25

Logging Multiple Values

You can pass multiple values to console.log() to print them in a single line.

Example

let firstName = "Amit";
let lastName = "Kumar";
let age = 25;
console.log(firstName, lastName, age);

Output:

Amit Kumar 25

Logging Objects and Arrays

The console.log() method can also be used to log objects and arrays, providing a clear and readable output.

Example

let person = {
  firstName: "Amit",
  lastName: "Kumar",
  age: 25
};

let numbers = [1, 2, 3, 4, 5];

console.log(person);
console.log(numbers);

Output:

{ firstName: 'Amit', lastName: 'Kumar', age: 25 }
[ 1, 2, 3, 4, 5 ]

Simple Programs using console.log()

Program 1: Debugging a Function

function add(a, b) {
  console.log("a:", a);
  console.log("b:", b);
  return a + b;
}

let result = add(5, 10);
console.log("Result:", result);

Output:

a: 5
b: 10
Result: 15

Program 2: Looping through an Array

let numbers = [10, 20, 30, 40, 50];

for (let i = 0; i < numbers.length; i++) {
  console.log("Index:", i, "Value:", numbers[i]);
}

Output:

Index: 0 Value: 10
Index: 1 Value: 20
Index: 2 Value: 30
Index: 3 Value: 40
Index: 4 Value: 50

Conclusion

In this chapter, you learned about the console.log() the method in JavaScript, including its basic usage, formatting output, logging multiple values, and logging objects and arrays. Understanding how to effectively use console.log() method is essential for debugging and testing your JavaScript code.