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Function in JavaScript

Anonymous User 304 19-Jul-2021

How to define and use a function in JavaScript? Can you explain with the help of an appropriate example?

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Updated on 29-Nov-2023
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Aryan Kumar

Aryan Kumar

29-Nov-2023

In JavaScript, functions are blocks of reusable code that can be defined and called to perform a specific task. Here's a basic overview of how functions work in JavaScript:

Defining a Function:

You can define a function using the function keyword, followed by the function name and a pair of parentheses. If the function takes parameters, you list them inside the parentheses. The code block that defines what the function does is enclosed in curly braces {}.

Example:

// Function without parameters
function greet() {
    console.log("Hello, there!");
}

// Function with parameters
function addNumbers(a, b) {
    return a + b;
}

Calling a Function:

Once a function is defined, you can call (invoke) it by using its name followed by parentheses. If the function takes parameters, you provide them within the parentheses.

Example:

// Calling the greet function
greet();

// Calling the addNumbers function with parameters
var result = addNumbers(5, 3);
console.log("Result:", result);

Function Expression:

You can also define functions using function expressions, which involve assigning a function to a variable.

Example:

// Function expression
var multiply = function(x, y) {
    return x * y;
};

// Calling the function expression
var product = multiply(4, 7);
console.log("Product:", product);

Arrow Functions (ES6+):

Arrow functions provide a more concise syntax for defining functions, especially for short, one-liner functions.

Example:

// Arrow function
const square = (num) => num * num;

// Calling the arrow function
var squaredValue = square(6);
console.log("Squared value:", squaredValue);

Anonymous Functions:

Functions without a name are called anonymous functions. They are often used as arguments to other functions or assigned to variables.

Example:

// Anonymous function as an argument
setTimeout(function() {
    console.log("This will run after 2 seconds.");
}, 2000);

Return Statement:

Functions can use the return statement to send a value back to the calling code. If no return statement is present, the function returns undefined by default.

Example:

// Function with a return statement
function multiplyByTwo(x) {
    return x * 2;
}

var result = multiplyByTwo(10);
console.log("Result:", result);

Understanding functions is fundamental to writing modular and organized JavaScript code. They allow you to encapsulate logic, promote code reuse, and make your code more maintainable.

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