Day 5: Understanding Functions in JavaScript

dipakahirav

Dipak Ahirav

Posted on June 14, 2024

Day 5: Understanding Functions in JavaScript

Introduction

Welcome to Day 5 of your JavaScript journey! Yesterday, we explored control structures, learning how to make decisions and repeat actions in our code. Today, we'll dive into functions, which are essential for organizing and reusing code in JavaScript.

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Functions

Functions are blocks of code designed to perform a particular task. They help to make your code more modular, reusable, and easier to read.

1. Function Declaration

A function declaration defines a function with the specified parameters.

Syntax:

function functionName(parameters) {
  // code to be executed
}
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Example:

function greet(name) {
  console.log("Hello, " + name + "!");
}

greet("Alice"); // Output: Hello, Alice!
greet("Bob");   // Output: Hello, Bob!
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2. Function Expression

A function expression defines a function as part of an expression. It can be anonymous or named.

Syntax:

const functionName = function(parameters) {
  // code to be executed
};
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Example:

const greet = function(name) {
  console.log("Hello, " + name + "!");
};

greet("Charlie"); // Output: Hello, Charlie!
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3. Arrow Functions

Arrow functions provide a shorter syntax for writing functions. They are anonymous and cannot be used as constructors.

Syntax:

const functionName = (parameters) => {
  // code to be executed
};
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Example:

const greet = (name) => {
  console.log("Hello, " + name + "!");
};

greet("Dave"); // Output: Hello, Dave!
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Parameters and Arguments

Functions can accept parameters, which are placeholders for the values you pass to the function (arguments).

Example:

function add(a, b) {
  return a + b;
}

let sum = add(5, 3);
console.log(sum); // Output: 8
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Return Statement

The return statement specifies the value to be returned by the function.

Example:

function multiply(a, b) {
  return a * b;
}

let product = multiply(4, 7);
console.log(product); // Output: 28
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Function Scope

Variables declared inside a function are local to that function and cannot be accessed outside it.

Example:

function scopeTest() {
  let localVar = "I am local";
  console.log(localVar); // Output: I am local
}

scopeTest();
// console.log(localVar); // Error: localVar is not defined
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Practical Examples

Example 1: Function to calculate the area of a rectangle

function calculateArea(width, height) {
  return width * height;
}

let area = calculateArea(5, 10);
console.log("Area:", area); // Output: Area: 50
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Example 2: Function to find the maximum of two numbers

function findMax(a, b) {
  if (a > b) {
    return a;
  } else {
    return b;
  }
}

let max = findMax(8, 12);
console.log("Max:", max); // Output: Max: 12
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Example 3: Arrow function to check if a number is even

const isEven = (number) => {
  return number % 2 === 0;
};

console.log(isEven(4)); // Output: true
console.log(isEven(7)); // Output: false
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Practice Activities

1. Practice Code:

  • Write functions using function declarations, function expressions, and arrow functions.
  • Create functions with parameters and return values.

2. Mini Project:

  • Create a simple script that takes a number from the user and uses a function to determine if the number is prime.

Example:

function isPrime(number) {
  if (number <= 1) {
    return false;
  }
  for (let i = 2; i < number; i++) {
    if (number % i === 0) {
      return false;
    }
  }
  return true;
}

let num = parseInt(prompt("Enter a number:"));
if (isPrime(num)) {
  console.log(num + " is a prime number.");
} else {
  console.log(num + " is not a prime number.");
}
// If the user enters 5, the output will be:
// 5 is a prime number.
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Summary

Today, we explored functions in JavaScript. We learned about function declarations, function expressions, and arrow functions. We also covered parameters, arguments, return statements, and function scope. Understanding functions is crucial for creating modular and reusable code.

Series Index

Part Title Link
1 Day 1: Getting Started with JavaScript Read Part 1
2 Day 2: Understanding Variables and Data Types in JavaScript Read Part 2
3 Day 3: Mastering Operators and Expressions in JavaScript Read Part 3
4 Day 4: Control Structures in JavaScript Read Part 4
5 Day 5: Understanding Functions in JavaScript Read Part 5
6 Day 6: Mastering Arrays in JavaScript ๐Ÿš€ Read Part 6
7 Day 7: Understanding Objects in JavaScript ๐Ÿ† Read Part 7

Stay tuned for Day 6, where we'll dive into arrays and their methods in JavaScript!

Feel free to leave your comments or questions below. If you found this guide helpful, please share it with your peers and follow me for more web development tutorials. Happy coding!

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dipakahirav
Dipak Ahirav

Posted on June 14, 2024

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