Lesson 5: Functions in JavaScript

Functions are blocks of code designed to perform a specific task. They help in organizing code into reusable pieces, which makes code more modular and easier to maintain.

Defining Functions

1. Function Declaration

A function declaration defines a named function. The function can be called from anywhere in the code after the declaration.

      function functionName(parameters) {
          // Code to execute
      }
          

Example of Function Declaration:

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

2. Function Expression

A function expression creates a function and assigns it to a variable. The function can only be called after it is defined.

      const functionName = function(parameters) {
          // Code to execute
      };
          

Example of Function Expression:

      const add = function(a, b) {
          return a + b;
      };
      
      console.log(add(5, 3)); // Output: 8
              

3. Arrow Functions

Arrow functions provide a shorter syntax for writing functions. They are often used for short functions and do not have their own this context.

      const functionName = (parameters) => {
          // Code to execute
      };
          

Example of Arrow Functions:

      const multiply = (x, y) => x * y;
      
      console.log(multiply(4, 5)); // Output: 20
              

Function Parameters and Return Values

1. Parameters

Parameters are variables listed as part of a function definition. They act as placeholders for values that are passed into the function.

      function greet(name, age) {
          console.log("Hello, " + name + ". You are " + age + " years old.");
      }
          

2. Return Values

The return statement ends function execution and specifies a value to be returned to the function caller.

      function square(number) {
          return number * number;
      }
      
      console.log(square(5)); // Output: 25