Lecture

Code Blocks for Specific Tasks: Functions

Functions are reusable blocks of code designed to perform specific tasks.

You create a function by using one or more lines of code enclosed in curly braces { } to form a block, and then you give this block a name.

Example of Function Definition
function sayHello() { console.log('Hello'); console.log('Nice to meet you'); }

In the example above, the function that prints the messages 'Hello' and 'Nice to meet you' is named sayHello.

The function contains two console.log commands within the curly braces { }, forming a single block.

When the function is called, the code inside the function is executed, printing the messages 'Hello' and 'Nice to meet you' on separate lines.

Function Call
function sayHello() { console.log('Hello'); console.log('Nice to meet you'); } sayHello(); // Hello // Nice to meet you

Why Use Functions?

The main goal of using functions is to enhance reusability of code.

Once a function is defined, it can be invoked multiple times using its name.

This reduces code duplication and improves maintainability.


How to Declare a Function

In JavaScript, functions are defined by using the function keyword, followed by the function name and parameters.

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

Here, add is the name of the function, and a and b are its parameters.

The curly braces { } contain the code that executes when the function is called, and the return keyword is used to yield the function's result.


How to Call a Function

Calling a function means executing the code inside it.

To call a function, append parentheses () to the function’s name.

Calling the add Function
const result = add(10, 20); // 30

In this example, add(10, 20) calls the add function, and 10 and 20 are the arguments passed to it.

Upon invocation, 10 and 20 are assigned to the function's parameters a and b, respectively, executing the code return a + b and returning 30.

The value 30 returned by return is stored in the constant result.


What's the Difference Between Parameters and Arguments?

Parameters are variables used internally when defining a function, whereas arguments are the actual values passed when a function is called.

multiply Function Returning the Product of Two Numbers
function multiply(a, b) { return a * b; } const result = multiply(2, 3); // 6

For instance, in the multiply function, a and b are the parameters, and the values 2 and 3 are the arguments passed during the function call.

Mission
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What keyword is used to define a function in JavaScript?

def

func

function

fnc

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