function ( ) / JavaScript

# Web Site Writing Basics

# javascript

# Function

Function in JavaScript is a block of reusable code designed to perform a particular task or process a certain value and send back the result (optional). 💡

Function is the most basic and important component in programming with JavaScript because it keeps code organized, easy to manage, and runs efficiently.

1. Main elements of the function

Functions in JavaScript include the following key parts:

Element, meaning, example (in function greet (name) {return "Hello," + name;})

Function name (name) The name used to call the greet function.

Parameters, a variable specified in parentheses that receives external entry values

Body (Body) A block of code inside the {} brace that will be processed when the function is called return "Hello," + name;

Return Value The value that the function sends back to the executed code (without the return command, it will automatically return undefined) returns "Hello," + name;

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2. Main benefits of the function

Reusability: We can write a set of instructions once and run it repeatedly in a program, reducing redundant code (Don't Repeat Yourself - DRY)

Organization: Helps break large code into functional subsections, making the code easier to read and manage (Modularity)

Debugging Ease: When an error occurs, the code can be checked and corrected one function at a time, narrowing the scope of the problem.

3. Function Syntax Format

JavaScript provides 3 main ways of creating functions:

3.1. function declaration (Function Declaration)

It is the most primitive and basic form. Functions created in this way are "elevated" (Hoisting) to the top of the scope (Scope), allowing the function to be called before the line declaring the function.

JavaScript

Function add (a, b) {

return a + b;

}

Let result = add (5, 3); / / Run immediately

3.2.Function expression (Function Expression)

Is to create an anonymous function and assign it to a variable:

JavaScript

Const subtract = function (a, b) {

return a - b;

};

Let result = subtract (10, 4); / / must be run only after the variable-defined line.

3.3.Arrow Functions (Arrow Functions - ES6)

It is a very short, concise and popular form of function writing today, using the symbol = > instead of the function:

JavaScript

/ / Basic format

Const times = (a, b) = > {

return a * b;

};

/ / Implict Return

/ / For a function that has a single command and needs to be restored.

const divide = (a, b) = > a / b;

Let result 1 = multiply (2, 4); / / 8

Let result 2 = divide (10, 2); / / 5

4. Relationship between function and JavaScript

In JavaScript, the function is considered a First-Class Citizen, which means:

Functions can be assigned to variables (as seen in Function Expression).

Functions can be sent as arguments to other functions (e.g. in Callback Functions).

A function can return another function as a result (e.g. in Higher-Order Functions).

This ability makes JavaScript very flexible and capable of programming in complex ways such as functional programming.